Servo Feedback Control Based on Designated Scanning Servo Beam in Scanning Beam Display Systems with Light-Emitting Screens

ABSTRACT

Scanning beam display systems that scan one servo beam and an excitation beam onto a screen that emits visible light under excitation of the light of the excitation beam and control optical alignment of the excitation beam based on positioning of the servo beam on the screen via a feedback control.

PRIORITY CLAIM AND RELATED PATENT APPLICATION

This patent document is a continuation of and claims priority to U.S.patent application Ser. No. 12/643,623 entitled “Servo Feedback ControlBased on Invisible Scanning Servo Beam in Scanning Beam Display Systemswith Light-Emitting Screens” filed Dec. 21, 2009, and is a continuationof and claims priority to International Application No.PCT/US2008/068679 entitled “Servo Feedback Control Based on DesignatedScanning Servo Beam in Scanning Beam Display Systems with Light-EmittingScreens” and filed Jun. 27, 2008, which designates U.S. and claimspriority from U.S. patent application Ser. No. 11/769,580 entitled“Servo Feedback Control Based on Invisible Scanning Servo Beam inScanning Beam Display Systems with Light-Emitting Screens” and filed onJun. 27, 2007. The disclosures of these applications are incorporated byreference as part of the specification of this document.

BACKGROUND

This patent application relates to scanning-beam display systems.

In a scanning-beam display system, an optical beam can be scanned over ascreen to form images on the screen. Many display systems such as laserdisplay systems use a polygon scanner with multiple reflective facets toprovide horizontal scanning and a vertical scanning mirror such as agalvo-driven mirror to provide vertical scanning. In operation, onefacet of the polygon scanner scans one horizontal line as the polygonscanner spins to change the orientation and position of the facet andthe next facet scans the next horizontal line. The horizontal scanningand the vertical scanning are synchronized to each other to projectimages on the screen.

SUMMARY

This patent application describes, among others, implementations ofdisplay systems and devices based on scanning light on a light-emittingscreen under optical excitation. The described display systems uselight-emitting screens under optical excitation and at least oneexcitation optical beam to excite one or more light-emitting materialson a screen which emit light to form images. Servo control mechanismsfor such display systems are described based on a designated servo beamthat is scanned over the screen by the same scanning module that scansthe image-carrying excitation optical beam. This designated servo beamis used to provide servo feedback control over the scanning excitationbeam to ensure proper optical alignment and accurate delivery of opticalpulses in the excitation beam during normal display operation. In someimplementations, multiple lasers can be used to simultaneously scanmultiple excitation laser beams on the screen. For example, the multiplelaser beams can illuminate one screen segment at a time and sequentiallyscan multiple screen segments to complete a full screen.

In one implementation, a scanning beam display system includes a lightmodule to direct and scan at least one excitation beam having opticalpulses that carry image information and at least one servo beam at aservo beam wavelength different from a wavelength of the excitationbeam; a screen positioned to receive the scanning excitation beam andthe servo beam and comprising a light-emitting layer of parallellight-emitting stripes which absorb light of the excitation beam to emitvisible light to produce images carried by the scanning excitation beam,the screen configured to reflect light of the servo beam towards thelight module to produce servo feedback light; and an optical servosensor module positioned to receive the servo feedback light and toproduce a servo feedback signal indicative of positioning of the servobeam on the screen. The light module is responsive to the positioning ofthe servo beam on the screen in the servo feedback signal to adjusttiming of the optical pulses carried by the scanning excitation beam tocontrol the spatial alignment of spatial positions of the optical pulsesin the excitation beam on the screen.

As an example, the screen in the above system can include servo feedbackmarks that have facets facing the excitation light source that arespecularly reflective to light of the servo beam, and areas outside theservo feedback marks that are diffusively reflective to light of theservo beam. In this example, the system includes a Fresnel lens locatedbetween the screen and the light module to direct the scanning servobeam and excitation beam to be at a substantially normal incidence tothe screen. The Fresnel lens has an optic axis symmetrically in a centerof the Fresnel lens to be parallel to and offset from an optic axis ofthe light module to direct light of the servo beam that is specularlyreflected by a servo feedback mark into the optical servo sensor whilelight of the servo beam that is diffusely reflected by the screenoutside a servo feedback mark is spread by the Fresnel lens over an areagreater than the optical servo sensor to direct a fraction of diffuselyreflected light of the servo beam into the optical servo sensor.

In another implementation, a method for controlling a scanning beamdisplay system includes scanning one or more excitation beams modulatedwith optical pulses to carry images on a screen to excite parallellight-emitting strips to emit visible light which forms the images;scanning a servo beam at an optical wavelength different from an opticalwavelength of the one or more excitation beams, on the screen; detectinglight of the servo beam from the screen to obtain a servo signalindicative of positioning of the servo beam on the screen; and, inresponse to the positioning of the servo beam on the screen, controllingthe one or more scanning excitation beams to control the spatialalignment of spatial positions of the optical pulses in each excitationbeam on the screen.

In another implementation, a scanning beam display system, includes anexcitation light source to produce at least one excitation beam havingoptical pulses that carry image information; a servo light source toproduce at least one servo beam at a servo beam wavelength that isinvisible; a beam scanning module to receive the excitation beam and theservo beam and to scan the excitation beam and the servo beam; and alight-emitting screen positioned to receive the scanning excitation beamand the servo beam. The screen includes a light-emitting area whichcomprises (1) parallel light-emitting stripes which absorb light of theexcitation beam to emit visible light to produce images carried by thescanning excitation beam, and (2) stripe dividers parallel to andspatially interleaved with the light-emitting stripes with each stripedivider being located between two adjacent stripes. Each stripe divideris optically reflective. An optical servo sensor is positioned toreceive light of the servo beam scanning on the screen including lightreflected by the stripe dividers and to produce a monitor signalindicative of positioning of the servo beam on the screen. This systemincludes a control unit operable to, in response to the positioning ofthe servo beam on the screen, adjust timing of the optical pulsescarried by the scanning excitation beam in response to the monitorsignal based on a relation between the servo beam and the excitationbeam to control the spatial alignment of spatial positions of theoptical pulses in the excitation beam on the screen.

In another implementation, a scanning beam display system includes alight-emitting screen comprising a light-emitting area which comprises(1) parallel light-emitting stripes which absorb excitation light toemit visible light, and (2) optically reflective stripe dividersparallel to and spatially interleaved with the light-emitting stripeswith each stripe divider being located between two adjacent stripes.Excitation lasers are provided to produce excitation laser beams of theexcitation light and at least one servo light source fixed in positionrelative to the excitation lasers is provided to produce at least oneservo beam at a servo beam wavelength that is invisible. This systemalso includes a beam scanning module to receive the excitation laserbeams and the servo beam and to scan the excitation laser beams and theservo beam; at least one first optical servo sensor positioned toreceive light of the servo beam reflected from the screen to produce afirst monitor signal indicative of positioning of the servo beam on thescreen; at least one second optical servo sensor positioned to receivelight of the excitation laser beams reflected from the screen to producea second monitor signal indicative of positioning of each excitationlaser beam on the screen; and a control unit operable to, in response tothe first and the second monitor signals, adjust timing of the opticalpulses carried by each excitation laser beam based on a relation betweenthe servo beam and each excitation laser beam to control the spatialalignment of spatial positions of the optical pulses in the excitationbeam on the screen.

In yet another implementation, a method for controlling a scanning beamdisplay system includes scanning at least one excitation beam modulatedwith optical pulses on a screen with parallel light-emitting stripes ina beam scanning direction perpendicular to the light-emitting stripes toexcite the fluorescent strips to emit visible light which forms images.The screen comprises stripe dividers parallel to and spatiallyinterleaved with the light-emitting stripes with each stripe dividerbeing located between two adjacent stripes and each stripe divider isoptically reflective. This method also includes: scanning a servo beam,which is invisible, along with the excitation beam on the screen;detecting light of the scanning servo beam from the screen includinglight produced by the stripe dividers to obtain a monitor signalindicative of positioning of the servo beam on the screen; and, inresponse to the positioning of the servo beam on the screen, adjustingtiming of the optical pulses carried by the scanning excitation beambased on a relation between the servo beam and the excitation beam tocontrol the spatial alignment of spatial positions of the optical pulsesin the excitation beam on the screen.

These and other examples and implementations are described in detail inthe drawings, the detailed description and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example scanning laser display system having alight-emitting screen made of laser-excitable light-emitting materials(e.g., phosphors) emitting colored lights under excitation of a scanninglaser beam that carries the image information to be displayed.

FIGS. 2A and 2B show one example screen structure with parallellight-emitting stripes and the structure of color pixels on the screenin FIG. 1.

FIG. 3 shows an example implementation of the laser display system inFIG. 1 in a pre-objective scanning configuration having multiple lasersthat direct multiple laser beams on the screen.

FIG. 4 shows an example implementation of a post-objective scanning beamdisplay system based on the laser display system in FIG. 1. FIG. 5 showsone example for simultaneously scanning consecutive scan lines withmultiple excitation laser beams and an invisible servo beam.

FIG. 5A shows a map of beam positions on the screen produced by a laserarray of thirty-six excitation lasers and one IR servo laser when avertical galvo scanner and a horizontal polygon scanner are at theirrespective null positions.

FIG. 6 shows one example of a scanning display system using a servofeedback control based on a scanning servo beam.

FIG. 7 shows an example of a servo detector for detecting the servofeedback light in FIG. 6.

FIGS. 8 and 9 show two screen examples for the servo control based on ascanning servo beam.

FIG. 10 shows optical power of servo light having optical signalscorresponding to stripe dividers on the screen.

FIG. 11 shows an example of a screen having peripheral reference markregions that include servo reference marks that produce feedback lightfor various servo control functions.

FIG. 12 shows a start of line reference mark in a peripheral referencemark region to provide a reference for the beginning of the activefluorescent area on the screen.

FIGS. 13 and 14 show optical power of servo light having optical signalscorresponding to stripe dividers, the start of line reference mark andend of line reference mark on the screen

FIGS. 15, 16 and 17 show examples of a use of a sampling clock signal tomeasure position data of stripe dividers on the screen using servofeedback light from the excitation beam or the servo beam.

FIG. 18A shows an example of a vertical beam position reference mark forthe screen in FIG. 11.

FIGS. 18B and 18C show a servo feedback control circuit and itsoperation in using the vertical beam position reference mark in FIG. 18Ato control the vertical beam position on the screen.

FIG. 19 shows an example of the screen in FIG. 11 having the start ofline reference mark and the vertical beam position reference marks.

FIG. 20 shows an operation of the servo control based on the servo beamthat is scanned with the excitation beam.

FIGS. 21, 22 and 23 show examples of screen designs that have IR servofeedback marks that do not affect the transmission amount of excitationbeams while having a property of diffuse or specular reflection for atleast the servo beams.

FIG. 24 shows an example of the screen design to have specularlyreflective IR feedback marks and diffusively reflective areas outsidethe IR feedback marks on the screen.

FIG. 25 shows an example of a system based on the design in FIG. 24.

FIG. 26 shows an example of a system that combines IR servo feedback andvisible light servo feedback.

FIGS. 27A-D, 28, 29 and 30 illustrate aspects of the system in FIG. 26.

FIG. 31 shows a system implementation of the system in FIG. 26.

DETAILED DESCRIPTION

Examples of scanning beam display systems in this application usescreens with light-emitting materials or fluorescent materials to emitlight under optical excitation to produce images, including laser videodisplay systems. Various examples of screen designs with light-emittingor fluorescent materials can be used. In one implementation, forexample, three different color phosphors that are optically excitable bythe laser beam to respectively produce light in red, green, and bluecolors suitable for forming color images may be formed on the screen aspixel dots or repetitive red, green and blue phosphor stripes inparallel.

Phosphor materials are one type of fluorescent materials. Variousdescribed systems, devices and features in the examples that usephosphors as the fluorescent materials are applicable to displays withscreens made of other optically excitable, light-emitting, non-phosphorfluorescent materials. For example, quantum dot materials emit lightunder proper optical excitation and thus can be used as the fluorescentmaterials for systems and devices in this application. Morespecifically, semiconductor compounds such as, among others, CdSe andPbS, can be fabricated in form of particles with a diameter on the orderof the exciton Bohr radius of the compounds as quantum dot materials toemit light. To produce light of different colors, different quantum dotmaterials with different energy band gap structures may be used to emitdifferent colors under the same excitation light. Some quantum dots arebetween 2 and 10 nanometers in size and include approximately tens ofatoms such between 10 to 50 atoms. Quantum dots may be dispersed andmixed in various materials to form liquid solutions, powders, jelly-likematrix materials and solids (e.g., solid solutions). Quantum dot filmsor film stripes may be formed on a substrate as a screen for a system ordevice in this application. In one implementation, for example, threedifferent quantum dot materials can be designed and engineered to beoptically excited by the scanning laser beam as the optical pump toproduce light in red, green, and blue colors suitable for forming colorimages. Such quantum dots may be formed on the screen as pixel dotsarranged in parallel lines (e.g., repetitive sequential red pixel dotline, green pixel dot line and blue pixel dot line).

Examples of scanning beam display systems described here use at leastone scanning laser beam to excite color light-emitting materialsdeposited on a screen to produce color images. The scanning laser beamis modulated to carry images in red, green and blue colors or in othervisible colors and is controlled in such a way that the laser beamexcites the color light-emitting materials in red, green and blue colorswith images in red, green and blue colors, respectively. Hence, thescanning laser beam carries the images but does not directly produce thevisible light seen by a viewer. Instead, the color light-emittingfluorescent materials on the screen absorb the energy of the scanninglaser beam and emit visible light in red, green and blue or other colorsto generate actual color images seen by the viewer.

Laser excitation of the fluorescent materials using one or more laserbeams with energy sufficient to cause the fluorescent materials to emitlight or to luminesce is one of various forms of optical excitation. Inother implementations, the optical excitation may be generated by anon-laser light source that is sufficiently energetic to excite thefluorescent materials used in the screen. Examples of non-laserexcitation light sources include various light-emitting diodes (LEDs),light lamps and other light sources that produce light at a wavelengthor a spectral band to excite a fluorescent material that converts thelight of a higher energy into light of lower energy in the visiblerange. The excitation optical beam that excites a fluorescent materialon the screen can be at a frequency or in a spectral range that ishigher in frequency than the frequency of the emitted visible light bythe fluorescent material. Accordingly, the excitation optical beam maybe in the violet spectral range and the ultra violet (UV) spectralrange, e.g., wavelengths under 420 nm. In the examples described below,Violet or a UV laser beam is used as an example of the excitation lightfor a phosphor material or other fluorescent material and may be lightat other wavelength.

FIG. 1 illustrates an example of a laser-based display system using ascreen having color phosphor stripes. Alternatively, color pixilatedlight-emitting areas may also be used to define the image pixels on thescreen. The system includes a laser module 110 to produce and project atleast one scanning laser beam 120 onto a screen 101. The screen 101 hasparallel color phosphor stripes in the vertical direction and twoadjacent phosphor stripes are made of different phosphor materials thatemit light in different colors. In the illustrated example, red phosphorabsorbs the laser light to emit light in red, green phosphor absorbs thelaser light to emit light in green and blue phosphor absorbs the laserlight to emit light in blue. Adjacent three color phosphor stripes arein three different colors. One particular spatial color sequence of thestripes is shown in FIG. 1 as red, green and blue. Other color sequencesmay also be used. The laser beam 120 is at the wavelength within theoptical absorption bandwidth of the color phosphors and is usually at awavelength shorter than the visible blue and the green and red colorsfor the color images. As an example, the color phosphors may bephosphors that absorb UV light in the spectral range below 420 nm toproduce desired red, green and blue light. The laser module 110 caninclude one or more lasers such as UV diode lasers to produce the beam120, a beam scanning mechanism to scan the beam 120 horizontally andvertically to render one image frame at a time on the screen 101, and asignal modulation mechanism to modulate the beam 120 to carry theinformation for image channels for red, green and blue colors. Suchdisplay systems may be configured as rear scanning systems where theviewer and the laser module 110 are on the opposite sides of the screen101. Alternatively, such display systems may be configured as frontscanning systems where the viewer and laser module 110 are on the sameside of the screen 101.

Examples of implementations of various features, modules and componentsin the scanning laser display system in FIG. 1 are described in U.S.patent application Ser. No. 10/578,038 entitled “Display Systems andDevices Having Screens With Optical Fluorescent Materials” and filed onMay 2, 2006 (U.S. Patent Publication No. 2008-0291140, PCT PatentApplication No. PCT/US2007/004004 entitled “Servo-Assisted Scanning BeamDisplay Systems Using Fluorescent Screens” and filed on Feb. 15, 2007(PCT Publication No. WO 2007/095329), PCT Patent Application No.PCT/US2007/068286 entitled “Phosphor Compositions For Scanning BeamDisplays” and filed on May 4, 2007 (PCT Publication No. WO 2007/131195),PCT Patent Application No. PCT/US2007/68989 entitled “MultilayeredFluorescent Screens for Scanning Beam Display Systems” and filed on May15, 2007 (PCT Publication No. WO 2007/134329), and PCT PatentApplication No. PCT/US2006/041584 entitled “Optical Designs for ScanningBeam Display Systems Using Fluorescent Screens” and filed on Oct. 25,2006 (PCT Publication No. WO 2007/050662). The disclosures of theabove-referenced patent applications are incorporated by reference intheir entirety as part of the specification of this application.

FIG. 2A shows an exemplary design of the screen 101 in FIG. 1. Thescreen 101 may include a rear substrate 201 which is transparent to thescanning laser beam 120 and faces the laser module 110 to receive thescanning laser beam 120. A second front substrate 202, is fixed relativeto the rear substrate 201 and faces the viewer in a rear scanningconfiguration. A color phosphor stripe layer 203 is placed between thesubstrates 201 and 202 and includes phosphor stripes. The color phosphorstripes for emitting red, green and blue colors are represented by “R”,“G” and “B,” respectively. The front substrate 202 is transparent to thered, green and blue colors emitted by the phosphor stripes. Thesubstrates 201 and 202 may be made of various materials, including glassor plastic panels. The rear substrate 201 can be a thin film layer andis configured to recycle the visible energy toward the viewer. Eachcolor pixel includes portions of three adjacent color phosphor stripesin the horizontal direction and its vertical dimension is defined by thebeam spread of the laser beam 120 in the vertical direction. As such,each color pixel includes three subpixels of three different colors(e.g., the red, green and blue). The laser module 110 scans the laserbeam 120 one horizontal line at a time, e.g., from left to right andfrom top to bottom to fill the screen 101. The relative alignment of thelaser module 110 and the screen 101 can be monitored and controlled toensure proper alignment between the laser beam 120 and each pixelposition on the screen 101. In one implementation, the laser module 110can be controlled to be fixed in position relative to the screen 101 sothat the scanning of the beam 120 can be controlled in a predeterminedmanner to ensure proper alignment between the laser beam 120 and eachpixel position on the screen 101.

In FIG. 2A, the scanning laser beam 120 is directed at the greenphosphor stripe within a pixel to produce green light for that pixel.FIG. 2B further shows the operation of the screen 101 in a view alongthe direction B-B perpendicular to the surface of the screen 101. Sinceeach color stripe is longitudinal in shape, the cross section of thebeam 120 may be shaped to be elongated along the direction of the stripeto maximize the fill factor of the beam within each color stripe for apixel. This may be achieved by using a beam shaping optical element inthe laser module 110. A laser source that is used to produce a scanninglaser beam that excites a phosphor material on the screen may be asingle mode laser or a multimode laser. The laser may also be a singlemode along the direction perpendicular to the elongated directionphosphor stripes to have a beam spread that is confined by and issmaller than the width of each phosphor stripe. Along the elongateddirection of the phosphor stripes, this laser beam may have multiplemodes to spread over a larger area than the beam spread in the directionacross the phosphor stripe. This use of a laser beam with a single modein one direction to have a small beam footprint on the screen andmultiple modes in the perpendicular direction to have a larger footprinton the screen allows the beam to be shaped to fit the elongated colorsubpixel on the screen and to provide sufficient laser power in the beamvia the multimodes to ensure sufficient brightness of the screen.

Referring now to FIG. 3, an example implementation of the laser module110 in FIG. 1 is illustrated. A laser array 310 with multiple lasers isused to generate multiple laser beams 312 to simultaneously scan thescreen 101 for enhanced display brightness. A signal modulationcontroller 320 is provided to control and modulate the lasers in thelaser array 310 so that the laser beams 312 are modulated to carry theimage to be displayed on the screen 101. The signal modulationcontroller 320 can include a digital image processor that generatesdigital image signals for the three different color channels and laserdriver circuits that produce laser control signals carrying the digitalimage signals. The laser control signals are then applied to modulatethe lasers, e.g., the currents for laser diodes, in the laser array 310.

The beam scanning can be achieved by using a scanning mirror 340 such asa galvo mirror for the vertical scanning and a multi-facet polygonscanner 350 for the horizontal scanning. A scan lens 360 can be used toproject the scanning beams form the polygon scanner 350 onto the screen101. The scan lens 360 is designed to image each laser in the laserarray 310 onto the screen 101. Each of the different reflective facetsof the polygon scanner 350 simultaneously scans N horizontal lines whereN is the number of lasers. In the illustrated example, the laser beamsare first directed to the galvo mirror 340 and then from the galvomirror 340 to the polygon scanner 350. The output scanning beams 120 arethen projected onto the screen 101. A relay optics module 330 is placedin the optical path of the laser beams 312 to modify the spatialproperty of the laser beams 312 and to produce a closely packed bundleof beams 332 for scanning by the galvo mirror 340 and the polygonscanner 350 as the scanning beams 120 projected onto the screen 101 toexcite the phosphors and to generate the images by colored light emittedby the phosphors. A relay optics module 370 is inserted between thescanners 340 and 350 to image the reflective surface of the reflector inthe vertical scanner 340 into a respective reflecting facet of thepolygon scanner 350 in order to prevent beam walk across the thin facetof the polygon scanner 350 in the vertical direction.

The laser beams 120 are scanned spatially across the screen 101 to hitdifferent color pixels at different times. Accordingly, each of themodulated beams 120 carries the image signals for the red, green andblue colors for each pixel at different times and for different pixelsat different times. Hence, the beams 120 are coded with imageinformation for different pixels at different times by the signalmodulation controller 320. The beam scanning thus maps the time-domaincoded image signals in the beams 120 onto the spatial pixels on thescreen 101. For example, the modulated laser beams 120 can have eachcolor pixel time equally divided into three sequential time slots forthe three color subpixels for the three different color channels. Themodulation of the beams 120 may use pulse modulation techniques toproduce desired grey scales in each color, a proper color combination ineach pixel, and desired image brightness.

In one implementation, the multiple beams 120 are directed onto thescreen 101 at different and adjacent vertical positions with twoadjacent beams being spaced from each other on the screen 101 by onehorizontal line of the screen 101 along the vertical direction. For agiven position of the galvo mirror 340 and a given position of thepolygon scanner 350, the beams 120 may not be aligned with each otheralong the vertical direction on the screen 101 and may be at differentpositions on the screen 101 along the horizontal direction. The beams120 can only cover one portion of the screen 101.

In one implementation, at an angular position of the galvo mirror 340,the spinning of the polygon scanner 350 causes the beams 120 from Nlasers in the laser array 310 to scan one screen segment of N adjacenthorizontal lines on the screen 101. The galvo mirror 340 tilts linearlyto change its tiling angle at a given rate along a vertical directionfrom the top towards the bottom during the scanning by the polygon untilthe entire screen 101 is scanned to produce a full screen display. Atthe end of the galvo vertical angular scan range, the galvo retraces toits top position and the cycle is repeated in synchronization with therefresh rate of the display.

In another implementation, for a given position of the galvo mirror 340and a given position of the polygon scanner 350, the beams 120 may notbe aligned with each other along the vertical direction on the screen101 and may be at different positions on the screen 101 along thehorizontal direction. The beams 120 can only cover one portion of thescreen 101. At a fixed angular position of the galvo mirror 340, thespinning of the polygon scanner 350 causes the beams 120 from N lasersin the laser array 310 to scan one screen segment of N adjacenthorizontal lines on the screen 101. At the end of each horizontal scanover one screen segment, the galvo mirror 340 is adjusted to a differentfixed angular position so that the vertical positions of all N beams 120are adjusted to scan the next adjacent screen segment of N horizontallines. This process iterates until the entire screen 101 is scanned toproduce a full screen display.

In the above example of a scanning beam display system shown in FIG. 3,the scan lens 360 is located downstream from the beam scanning devices340 and 350 and focuses the one or more scanning excitation beams 120onto the screen 101. This optical configuration is referred to as a“pre-objective” scanning system. In such a pre-objective design, ascanning beam directed into the scan lens 360 is scanned along twoorthogonal directions. Therefore, the scan lens 360 is designed to focusthe scanning beam onto the screen 101 along two orthogonal directions.In order to achieve the proper focusing in both orthogonal directions,the scan lens 360 can be complex and, often, are made of multiples lenselements. In one implementation, for example, the scan lens 360 can be atwo-dimensional f-theta lens that is designed to have a linear relationbetween the location of the focal spot on the screen and the input scanangle (theta) when the input beam is scanned around each of twoorthogonal axes perpendicular to the optic axis of the scan lens. Thetwo-dimensional scan lens 360 such as a f-theta lens in thepre-objective configuration can exhibit optical distortions along thetwo orthogonal scanning directions which cause beam positions on thescreen 101 to trace a curved line. The scan lens 360 can be designedwith multiple lens elements to reduce the bow distortions and can beexpensive to fabricate.

To avoid the above distortion issues associated with a two-dimensionalscan lens in a pre-objective scanning beam system, a post-objectivescanning beam display system can be implemented to replace thetwo-dimensional scan lens 360 with a simpler, less expensive1-dimensional scan lens. U.S. patent application Ser. No. 11/742,014entitled “POST-OBJECTIVE SCANNING BEAM SYSTEMS” and filed on Apr. 30,2007 (U.S. Patent Publication No. 2008-0247020 describes examples ofpost-objective scanning beam systems suitable for use with phosphorscreens described in this application and is incorporated by referenceas part of the specification of this application.

FIG. 4 shows an example implementation of a post-objective scanning beamdisplay system based on the system design in FIG. 1. A laser array 310with multiple lasers is used to generate multiple laser beams 312 tosimultaneously scan a screen 101 for enhanced display brightness. Asignal modulation controller 320 is provided to control and modulate thelasers in the laser array 310 so that the laser beams 312 are modulatedto carry the image to be displayed on the screen 101. The beam scanningis based on a two-scanner design with a horizontal scanner such as apolygon scanner 350 and a vertical scanner such as a galvanometerscanner 340. Each of the different reflective facets of the polygonscanner 350 simultaneously scans N horizontal lines where N is thenumber of lasers. A relay optics module 330 reduces the spacing of laserbeams 312 to form a compact set of laser beams 332 that spread withinthe facet dimension of the polygon scanner 350 for the horizontalscanning. Downstream from the polygon scanner 350, there is a 1-Dhorizontal scan lens 380 followed by a vertical scanner 340 (e.g., agalvo mirror) that receives each horizontally scanned beam 332 from thepolygon scanner 350 through the 1-D scan lens 380 and provides thevertical scan on each horizontally scanned beam 332 at the end of eachhorizontal scan prior to the next horizontal scan by the next facet ofthe polygon scanner 350. The vertical scanner 340 directs the 2-Dscanning beams 390 to the screen 101.

Under this optical design of the horizontal and vertical scanning, the1-D scan lens 380 is placed downstream from the polygon scanner 140 andupstream from the vertical scanner 340 to focus each horizontal scannedbeam on the screen 101 and minimizes the horizontal bow distortion todisplayed images on the screen 101 within an acceptable range, thusproducing a visually “straight” horizontal scan line on the screen 101.Such a 1-D scan lens 380 capable of producing a straight horizontal scanline is relatively simpler and less expensive than a 2-D scan lens ofsimilar performance. Downstream from the scan lens 380, the verticalscanner 340 is a flat reflector and simply reflects the beam to thescreen 101 and scans vertically to place each horizontally scanned beamat different vertical positions on the screen 101 for scanning differenthorizontal lines. The dimension of the reflector on the vertical scanner340 along the horizontal direction is sufficiently large to cover thespatial extent of each scanning beam coming from the polygon scanner 350and the scan lens 380. The system in FIG. 4 is a post-objective designbecause the 1-D scan lens 380 is upstream from the vertical scanner 340.In this particular example, there is no lens or other focusing elementdownstream from the vertical scanner 340.

Notably, in the post-objective system in FIG. 4, the distance from thescan lens to a location on the screen 101 for a particular beam varieswith the vertical scanning position of the vertical scanner 340.Therefore, when the 1-D scan lens 380 is designed to have a fixed focaldistance along the straight horizontal line across the center of theelongated 1-D scan lens, the focal properties of each beam must changewith the vertical scanning position of the vertical scanner 380 tomaintain consistent beam focusing on the screen 101. In this regard, adynamic focusing mechanism can be implemented to adjust convergence ofthe beam going into the 1-D scan lens 380 based on the vertical scanningposition of the vertical scanner 340.

For example, in the optical path of the one or more laser beams from thelasers to the polygon scanner 350, a stationary lens and a dynamicrefocus lens can be used as the dynamic focusing mechanism. Each beam isfocused by the dynamic focus lens at a location upstream from thestationary lens. When the focal point of the lens coincides with thefocal point of the lens, the output light from the lens is collimated.Depending on the direction and amount of the deviation between the focalpoints of the lenses, the output light from the collimator lens towardthe polygon scanner 350 can be either divergent or convergent. Hence, asthe relative positions of the two lenses along their optic axis areadjusted, the focus of the scanned light on the screen 101 can beadjusted. A refocusing lens actuator can be used to adjust the relativeposition between the lenses in response to a control signal. In thisparticular example, the refocusing lens actuator is used to adjust theconvergence of the beam directed into the 1-D scan lens 380 along theoptical path from the polygon scanner 350 in synchronization with thevertical scanning of the vertical scanner 340. The vertical scanner 340in FIG. 4 scans at a much smaller rate than the scan rate of the firsthorizontal scanner 350 and thus a focusing variation caused by thevertical scanning on the screen 101 varies with time at the slowervertical scanning rate. This allows a focusing adjustment mechanism tobe implemented in the system of FIG. 1 with the lower limit of aresponse speed at the slower vertical scanning rate rather than the highhorizontal scanning rate.

The beams 120 on the screen 101 are located at different and adjacentvertical positions with two adjacent beams being spaced from each otheron the screen 101 by one horizontal line of the screen 101 along thevertical direction. For a given position of the galvo mirror 540 and agiven position of the polygon scanner 550, the beams 120 may not bealigned with each other along the vertical direction on the screen 101and may be at different positions on the screen 101 along the horizontaldirection. The beams 120 can cover one portion of the screen 101.

FIG. 5 illustrates the above simultaneous scanning of one screen segmentwith multiple scanning laser beams 120 at a time. Visually, the beams120 behaves like a paint brush to “paint” one thick horizontal strokeacross the screen 101 at a time to cover one screen segment between thestart edge and the end edge of the image area of the screen 101 and thensubsequently to “paint” another thick horizontal stroke to cover anadjacent vertically shifted screen segment. Assuming the laser array 310has N=36 lasers, a 1080-line progressive scan of the screen 101 wouldrequire scanning 30 vertical screen segments for a full scan. Hence,this configuration in an effect divides the screen 101 along thevertical direction into multiple screen segments so that the N scanningbeams scan one screen segment at a time with each scanning beam scanningonly one line in the screen segment and different beams scanningdifferent sequential lines in that screen segment. After one screensegment is scanned, the N scanning beams are moved at the same time toscan the next adjacent screen segment.

In the above design with multiple laser beams, each scanning laser beam120 scans only a number of lines across the entire screen along thevertical direction that is equal to the number of screen segments.Hence, the polygon scanner 550 for the horizontal scanning can operateat slower speeds than scanning speeds required for a single beam designwhere the single beam scans every line of the entire screen. For a givennumber of total horizontal lines on the screen (e.g., 1080 lines inHDTV), the number of screen segments decreases as the number of thelasers increases. Hence, with 36 lasers, the galvo mirror and thepolygon scanner scan 30 lines per frame while a total of 108 lines perframe are scanned when there are only 10 lasers. Therefore, the use ofthe multiple lasers can increase the image brightness which isapproximately proportional to the number of lasers used, and, at thesame time, can also advantageously reduce the speed of the scanningsystem.

A scanning display system described in this specification can becalibrated during the manufacture process so that the laser beam on-offtiming and position of the laser beam relative to the fluorescentstripes in the screen 101 are known and are controlled within apermissible tolerance margin in order for the system to properly operatewith specified image quality. However, the screen 101 and components inthe laser module 101 of the system can change over time due to variousfactors, such as scanning device jitter, changes in temperature orhumidity, changes in orientation of the system relative to gravity,settling due to vibration, aging and others. Such changes can affect thepositioning of the laser source relative to the screen 101 over time andthus the factory-set alignment can be altered due to such changes.Notably, such changes can produce visible and, often undesirable,effects on the displayed images. For example, a laser pulse in thescanning excitation beam 120 may hit a subpixel that is adjacent to anintended target subpixel for that laser pulse due to a misalignment ofthe scanning beam 120 relative to the screen along the horizontalscanning direction. When this occurs, the coloring of the displayedimage is changed from the intended coloring of the image. Hence, a redpixel in the intended image may be displayed as a green pixel on thescreen. For another example, a laser pulse in the scanning excitationbeam 120 may hit both the intended target subpixel and an adjacentsubpixel next to the intended target subpixel due to a misalignment ofthe scanning beam 120 relative to the screen along the horizontalscanning direction. When this occurs, the coloring of the displayedimage is changed from the intended coloring of the image and the imageresolution deteriorates. The visible effects of these changes canincrease as the screen display resolution increases because a smallerpixel means a smaller tolerance for a change in position. In addition,as the size of the screen increases, the effect of a change that canaffect the alignment can be more pronounced because a large moment armin scanning each excitation beam 120 associated with a large screenmeans that an angular error can lead to a large position error on thescreen. For example, if the laser beam position on the screen for aknown beam angle changes over time, the result is a color shift in theimage. This effect can be noticeable and thus undesirable to the viewer.

Implementations of various alignment mechanisms are provided in thisspecification to maintain proper alignment of the scanning beam 120 onthe desired sub-pixel to achieved desired image quality. These alignmentmechanisms include reference marks on the screen, both in thefluorescent area and in one or more peripheral area outside thefluorescent area, emitted visible light in red, green and blue colors bythe phosphor stripes to provide feedback light that is caused by theexcitation beam 120 and represents the position and other properties ofthe scanning beam on the screen. The feedback light can be measured byusing one or more optical servo sensors to produce one or more feedbackservo signals and such feedback servo signals are used to generate alocation map for red, green and blue sub-pixels on the screen. A servocontrol in the laser module 110 processes this feedback servo signal toextract the information on the beam positioning and other properties ofthe beam on the screen and, in response, adjust the direction and otherproperties of the scanning beam 120 to ensure the proper operation ofthe display system.

For example, a feedback servo control system can be provided to useperipheral servo reference marks positioned outside the display areaunobservable by the viewer to provide control over various beamproperties, such as the horizontal positioning along the horizontalscanning direction perpendicular to the fluorescent stripes, thevertical positioning along the longitudinal direction of the fluorescentstripes, the beam focusing on the screen for control of image color(e.g., color saturation) and image sharpness, and the beam power on thescreen for control of image brightness and uniformity of the imagebrightness across the screen. For another example, a screen calibrationprocedure can be performed at the startup of the display system tomeasure the beam position information as a calibration map so having theexact positions of sub-pixels on the screen in the time domain. Thiscalibration map is then used by the laser module 110 to control thetiming and positioning of the scanning beam 120 to achieve the desiredcolor purity. For yet another example, a dynamic servo control systemcan be provided to regularly update the calibration map during thenormal operation of the display system by using servo reference marks inthe fluorescent area of the screen to provide the feedback light withoutaffecting the viewing experience of a viewer. Examples for using servolight produced by phosphor stripe dividers from the excitation light andfeedback light from other reference marks for servo control and screencalibration are described in the incorporated-by-reference PCT PatentApplication No. PCT/US2007/004004 entitled “Servo-Assisted Scanning BeamDisplay Systems Using Fluorescent Screens” (PCT Publication No. WO2007/095329).

The display systems in this application provide servo control mechanismsbased on a designated servo beam that is scanned over the screen by thesame scanning module that scans the image-carrying excitation opticalbeam. This designated servo beam is used to provide servo feedbackcontrol over the scanning excitation beam to ensure proper opticalalignment and accurate delivery of optical pulses in the excitation beamduring normal display operation. This designated servo beam has anoptical wavelength different from that of the excitation beam. As anexample, this designated servo beam can be an IR servo beam that may beinvisible to human. The examples below use an IR servo beam 130 toillustrate features and operations of this designated servo beam.

Referring to FIG. 1, the laser module 110 produces an invisible servobeam 130 such as an IR beam as an example of the designated servo beam.The laser module 110 scans the servo beam 130 on to the screen 101 alongwith the excitation beam 120. Different from the excitation beam 120,the servo beam 130 is not modulated to carry image data. The servo beam130 can be a CW beam. The stripe dividers on the screen 101 can be madereflective to the light of the servo beam 130 and to produce feedbacklight 132 by reflection. The servo beam 130 has a known spatial relationwith the excitation beam 120. Therefore, the positioning of the servobeam 130 can be used to determine the positioning of the excitation beam120. This relationship between the servo beam 130 and the excitationbeam 120 can be determined by using reference servo marks such as astart of line (SOL) mark in a non-viewing area of the screen 101. Thelaser module 101 receives and detects the feedback light 132 to obtainpositioning information of the servo beam 130 on the screen 101 and usesthis positioning information to control alignment of the excitation beam120 on the screen.

The servo beam 130 is invisible to human and thus does not produce anynoticeable visual artifact on the screen 101 during the normal operationof the system when images are produced on the screen 101. For example,the servo beam 130 can have a wavelength in a range from 780 nm to 820nm. For safety concerns, the screen 101 can be made to have a filterthat blocks the invisible servo beam 130 from exiting the screen 101 onthe viewer side. In this regard, a cutoff absorbing filter with abandpass transmission range only in the visible spectral range (e.g.,from 420 nm to 680 nm) may be used to block the servo beam 130 andexcitation beam 120. The servo control of the excitation beam 120 basedon the servo beam 130 can be performed dynamically during the normaloperation of the system. This servo design avoids manipulation of theimage-producing excitation beam 120 during the normal display mode forservo operations and thus avoids any visual artifacts that may be causedby the servo-related manipulation of the image-producing excitation beam120.

In addition, the scattered or reflected excitation light by the screen101 may also be used for servo control operations during a period whenthe system does not show images, e.g., during the startup period of thesystem or when the excitation beam 120 is outside the active displayarea of the screen 101. In such a case, the scattered or reflectedexcitation light, labeled as light 122, can be used as servo feedbacklight for servo control of, e.g., the horizontal alignment or thevertical alignment of each laser beam 120.

In the examples of the systems in FIGS. 3 and 4, the servo beam 130 isdirected along with the one or more excitation beams 120 through thesame optical path that includes the relay optics module 330A or 330B,the beam scanners 340 and 350, and the scan lens 360 or 380. Referringto FIG. 5, the servo beam 130 is scanned along with the scanningexcitation beams 120 one screen segment at a time along the verticaldirection of the screen. The servo beam 130 is invisible and can beoverlapped with a scanning path of one excitation beam 120 or along itsown scanning path that is different from a path of any of the excitationbeams 120. The spatial relation between the servo beam 130 and eachexcitation beam 120 is known and fixed so that the positioning of theservo beam 130 on the screen 101 can be used to infer positioning ofeach excitation beam 120.

A light source for generating the servo beam 130 and a light source forgenerating an excitation beam 120 can be semiconductor lasers in a lightsource module which can be an array of lasers and at least one of thelasers in the laser array can be a servo laser that produces the servobeam 130. In one implementation, the location of the servo laser isknown relative to each excitation laser in the laser array in the lasermodule 110. The servo beam 130 and each excitation beam 120 are directedthrough the same relay optics, the same beam scanners and the sameprojection lens and are projected on the screen 101. Therefore, thepositioning of the servo beam 130 on the screen 101 has a known relationwith the positioning of each excitation beam 120 on the screen. Thisrelation between the servo beam 130 and each excitation beam 120 can beused to control the excitation beam 120 based on measured positioning ofthe servo beam 130. The relative position relation between the servobeam 130 and each excitation beam 120 can be measured using the servofeedback, e.g., during a calibration process that may be separatelyperformed or performed during the power-up period of the system. Themeasured relative position relation is used for the servo feedbackcontrol.

FIG. 5A shows a map of beam positions on the screen produced by a laserarray of thirty-six excitation lasers and one IR servo laser when avertical galvo scanner and a horizontal polygon scanner are at theirrespective null positions in a prototype pre-objective scanning displaysystem. The thirty-six excitation lasers are arranged in a 4×9 laserarray and the IR servo laser is placed in the center of the laser array.The laser beams occupy an area of about 20 mm×25 mm on the screen. Inthis example, the vertical spacing is one half of a pixel between twovertically adjacent excitation lasers and the horizontal spacing betweentwo adjacent excitation lasers is 3.54 pixels. Because the excitationlasers are spatially staggered along both horizontal and verticaldirections, each scan in one screen segment produces thirty-sixhorizontal lines on the screen occupying thirty-six pixels along thevertical direction. In operation, these thirty-seven laser beams arescanned together based on the scanning shown in FIG. 5 to scan onescreen segment at a time to sequentially scan different screen segmentsat different vertical positions to scan the entire screen. Because theIR servo laser is fixed in position with respect to each and every oneof the thirty-six excitation lasers, the positioning of the servo beam130 produced by the IR servo laser on the screen 101 has a knownrelation with respect to each beam spot of an excitation beam 120 fromeach of the thirty-six excitation lasers.

FIG. 6 illustrates a scanning beam display system based on a servocontrol using the invisible servo beam 130. A display processor andcontroller 640 can be used to provide control functions and controlintelligence based on servo detector signals from radiation servodetectors 620 that detect servo feedback light 132 from the screen 101.A single detector 620 may be sufficient and two or more servo detectors620 can be used to improve the servo detection sensitivity.

Similarly, one or more radiation servo detectors 630 may also be used tocollect excitation servo light 122 produced by scattering or reflectingthe excitation beam 120 at the screen to provide additional feedbacksignals to the processor and controller 640 for the servo control. Thisuse of the servo light 122 for feedback control can be an optionalfeature that is used in combination with the IR servo feedback control.In some system implementations, the IR servo feedback alone without thefeedback based on the feedback light 122 shown in FIG. 6 can besufficient to align the excitation beam 120 to the proper phosphorstripes on the screen 101. Examples for using the servo light 122produced by phosphor stripe dividers for servo control are described inthe incorporated-by-reference PCT Patent Application No.PCT/US2007/004004 entitled “Servo-Assisted Scanning Beam Display SystemsUsing Fluorescent Screens” (PCT Publication No. WO 2007/095329).

In FIG. 6, a scanning projection module 610 is provided to scan andproject the excitation and servo beams 120 and 130 onto the screen 101.The module 610 can be in a post-objective configuration or apre-objective configuration. As illustrated, the image data is fed tothe display processor and controller 640 which produces an image datasignal carrying the image data to the signal modulator controller 520for the excitation lasers 510. The servo laser which is among theexcitation lasers in the array 510 is not modulated to carry image data.The signal modulation controller 520 can include laser driver circuitsthat produce laser modulation signals carrying image signals with imagedata assigned to different lasers 510, respectively. The laser controlsignals are then applied to modulate the lasers in the laser array 510,e.g., the currents for laser diodes to produce the laser beams 512. Thedisplay processor and controller 640 also produces laser control signalsto the lasers in the laser array 510 to adjust the laser orientation tochange the vertical beam position on the screen 101 or the DC powerlevel of each laser. The display processor and controller 5930 furtherproduces scanning control signals to the scanning projection module 610to control and synchronize the horizontal polygon scanner and thevertical scanner.

FIG. 7 shows one example of the servo detector design where a servodetector 620 detects the servo feedback light 132. The servo detector620 can be a detector designed to be sensitive to light of the servobeam wavelength for the invisible servo beam 130 and less sensitive toother light such as the visible light and the excitation light. Anoptical filter 710 can be used to filter the light from the screen 101to selectively transmit the servo feedback light 132 while blockinglight at other wavelengths, such as the excitation light and visiblelight. Such a filter allows a wider range of optical detectors to beused as the servo detector. FIG. 7 also shows an example of an optionalservo detector 630 for detecting the servo feedback light 122 at theexcitation wavelength. The servo detector 620 can be a detector designedto be sensitive to light of the excitation wavelength of the excitationbeam 120 and less sensitive to light at wavelengths of the servo beam130 and the visible light emitted by the screen 101. An optical filter720 can be used to filter the light from the screen 101 to selectivelytransmit the excitation servo feedback light 122 while blocking light atother wavelengths. The servo detector signals 721 and 722 from the servodetectors 620 and 630, respectively, are directed to the processor andcontroller 640 for servo control operations.

FIGS. 8 and 9 show two exemplary screen designs for the screen 101 forproviding the feedback light 122 and 132. In FIG. 8, each strip divider810 is made optically reflective to the servo and excitation beams sothe reflection can be used as the feedback light 132. The strip divider810 can also be made reflective and opaque to light to optically isolateadjacent light-emitting stripes to enhance contrast and to reduce crosstalk. The light-emitting stripes such phosphor stripes emitting red,green and blue light are less reflective to the servo and excitationbeams than the stripe dividers 810 so that the feedback light 132exhibits a spike every time the servo or excitation beams 130 passthrough a stripe divider 810. An absorbent black layer 820 can be coatedon each stripe divider on the viewer side to reduce glare of ambientlight to the viewer. FIG. 9 shows another screen design where areflective servo reference mark 910 is formed on the excitation side ofeach strip divider 901, e.g., a reflective stripe coating.

In each horizontal scan, the beam 120 or 130 scans across thelight-emitting stripes and the reflections produced by the stripedividers can be used to indicate horizontal positions of the stripedividers, spacing between two adjacent stripe dividers and horizontalpositions of the horizontally scanned beam 120 or 130. Therefore,reflections from the stripe dividers can be used for servo control ofthe horizontal alignment between the beam 120 and the light-emittingstrips.

FIG. 10 shows operation of the stripe dividers as alignment referencemarks. As the servo beam 120 or 130 is scanned horizontally across thescreen 101 and the light at the servo beam shows a low power when theservo beam 130 is at a light-emitting stripe and a high power when theservo beam is at a stripe divider. When the beam spot of the servo beam130 on the screen 101 is less than the width of one subpixel, the powerof the servo light shows a periodic pattern in each horizontal scanwhere the high power peak corresponds to a stripe divider. This patterncan be used to measure the position of the stripe dividers or the widthof each stripe divider based on clock cycles of a clocking signal in theprocessor and controller 640. This measured information is used toupdate a positioning map of each excitation beam 120 in the horizontalscan. When the beam spot of the servo beam 130 is greater than one widthof the subpixel but is less than one color pixel made up by threeadjacent subpixels, the power of the servo light 132 still shows aperiodic pattern in each horizontal scan where the high power peakcorresponds to one color pixel and thus can be used for servo control.

In addition to the stripe dividers as alignment reference marks on thescreen 101, additional alignment reference marks can be implemented todetermine the relative position of the beam and the screen and otherparameters of the excitation beam on the screen. For example, during ahorizontal scan of the excitation and servo beams across thelight-emitting stripes, a start of line mark can be provided for thesystem to determine the beginning of the active light-emitting displayarea of the screen 101 so that the signal modulation controller of thesystem can properly control the timing in delivering optical pulses totargeted pixels. An end of line mark can also be provided for the systemto determine the end of the active light-emitting display area of thescreen 101 during a horizontal scan. For another example, a verticalalignment referenced mark can be provided for the system to determinewhether the scanning beams are pointed to a proper vertical location onthe screen. Other examples for reference marks may be one or morereference marks for measuring the beam spot size on the screen and oneor more reference marks on the screen to measure the optical power ofthe excitation beam 120. Such reference marks can be placed a regionoutside the active fluorescent area of the screen 101, e.g., in one ormore peripheral regions of the active fluorescent screen area and areused for both excitation and servo beams.

FIG. 11 illustrates one example of a fluorescent screen 101 havingperipheral reference mark regions. The screen 101 includes a centralactive light-emitting display area 1100 with parallel fluorescentstripes for displaying images, two stripe peripheral reference markregions 1110 and 1120 that are parallel to the fluorescent stripes. Eachperipheral reference mark region can be used to provide variousreference marks for the screen 101. In some implementations, only theleft peripheral reference mark region 1110 is provided without thesecond region 1120 when the horizontal scan across the fluorescentstripes is directed from the left to the right of the area 1100.

Such a peripheral reference mark region on the screen 101 allows thescanning display system to monitor certain operating parameters of thesystem. A reference mark in the peripheral reference mark region can beused for a servo control operation based on the servo feedback light 132generated from the servo beam 130. When the servo feedback light 122generated from the excitation beam 120 is also used for a servo controloperation, a reference mark in the peripheral reference mark region canbe used for servo control operation based on the servo feedback light122. A reference mark in the peripheral reference mark region can beused to measure both the excitation beam 120 and the servo beam 130 fora servo control operation in some implementations. The description onvarious examples of reference marks below may specifically refer to theexcitation beam 120 and similar functions can be used in connection withthe servo beam 130.

Notably, a reference mark in the peripheral reference mark region isoutside the active display area 1100 of the screen 101 and thus acorresponding servo feedback control function can be performed outsidethe duration during the display operation when the excitation beam isscanning through the active fluorescent display area 2600 to displayimage. Therefore, a dynamic servo operation can be implemented withoutinterfering with the display of the images to the viewer. In thisregard, each scan can include a continuous mode period when anexcitation beam sans through the peripheral referenced mark region forthe dynamic servo sensing and control and a display mode period when themodulation of the excitation beam is turned on to produce image-carryingoptical pulses as the excitation beam scans through the activefluorescent display area 1100. The servo beam 130 is not modulated tocarry image data and thus can be a continuous beam with a constant beampower when incident onto the screen 101. The power of the reflectedservo light in the feedback light 132 is modulated by the referencemarks and stripe dividers and other screen pattern on the screen 101.The modulated power of the reflected servo light can be used to measurethe location of the servo beam 130 on the screen 101.

FIG. 12 shows an example of a start of line (SOL) reference mark 1210 inthe left peripheral region 1110 in the screen 101. The SOL referencemark 1210 can be an optically reflective, diffusive or fluorescentstripe parallel to the fluorescent stripes in the active light-emittingregion 1100 of the screen 101. The SOL reference mark 1210 is fixed at aposition with a known distance from the first fluorescent stripe in theregion 1100. SOL patterns may be a single reflective stripe in someimplementations and may include multiple vertical lines with uniform orvariable spacing in other implementations. Multiple lines are selectedfor redundancy, increasing the signal to noise ratio, accuracy ofposition (time) measurement, and providing missing pulse detection.

In operation, the scanning excitation beam 120 is scanned from the leftto the right in the screen 101 by first scanning through the peripheralreference mark region 1110 and then through the active region 1100. Whenthe beam 120 is in the peripheral reference mark region 1110, the signalmodulation controller in the laser module 110 of the system sets thebeam 120 in a mode that ensures adequate sampling of information withoutcrosstalk (e.g. one beam at a time during one frame) When the scanningexcitation beam 120 scans through the SOL reference mark 1210, the lightreflected, scattered or emitted by the SOL reference mark 1210 due tothe illumination by the excitation beam 1210 can be measured at an SOLoptical detector located near the SOL reference mark 1210. The presenceof this signal indicates the location of the beam 120. The SOL opticaldetector can be fixed at a location in the region 1110 on the screen 101or off the screen 101. Therefore, the SOL reference mark 1210 can beused to allow for periodic alignment adjustment during the lifetime ofthe system.

When the pulse from the SOL 1210 detected is detected for a givenexcitation beam, the laser can be controlled to, after the delayrepresenting the time for scanning the beam from the SOL 1210 to theleft edge of the active display area 1100, operate in the image mode andcarry optical pulses with imaging data. The system then recalls apreviously measured value for the delay from SOL pulse to beginning ofthe image area 1100. This process can be implemented in each horizontalscan to ensure that each horizontal line starts the image area properlyand optical pulses in each horizontal scan are aligned to thelight-emitting stripes. The correction is made prior to painting theimage for that line in the area 1100 on the screen 101, so there is notime lag in displaying the images caused by the servo control. Thisallows for both high frequency (up to line scan rate) and low frequencyerrors to be corrected.

The servo beam 130 can be used to provide a positioning reference foreach excitation beam 120 for controlling both the timing for beginningimage-carrying pulses before the excitation beam enters the activelight-emitting area 1100 and during the normal display when theexcitation beam 120 scans in the active light-emitting region 1100. FIG.13 illustrates the detected signal power of the light at the servo beamwavelength in the feedback light 132 to show optical signals indicativeof positions of the SOL mark and stripe dividers on the screen 101. Theoptical peaks in the feedback light shown in FIGS. 13 and 14 areidealized as sharp square wave signals and are likely to have tailingand leading profiles shown in FIGS. 15-16. Such a pulse signal withtrailing and leading profiles can be converted into square wave likepulse signals by edge detection.

Similar to the SOL mark 1210, an end-of-line (EOL) reference mark can beimplemented on the opposite side of the screen 101, e.g., in theperipheral reference mark region 1120 in FIG. 11. The SOL mark is usedto ensure the proper alignment of the laser beam with the beginning ofthe image area. This does not ensure the proper alignment during theentire horizontal scan because the position errors can be present acrossthe screen. Implementing the EOL reference mark and an end-of-lineoptical detector in the region 1120 can be used to provide a linear, twopoint correction of laser beam position across the image area. FIG. 14illustrates the detected signal power of the light at the servo beamwavelength in the feedback light 132 to show optical signals indicativeof positions of the SOL mark, stripe dividers and EOL mark on the screen101

When both SOL and EOL marks are implemented, the laser is turned oncontinuously in a continuous wave (CW) mode prior to reaching the EOLsensor area. Once the EOL signal is detected, the laser can be returnedto image mode and timing (or scan speed) correction calculations aremade based on the time difference between the SOL and EOL pulses. Thesecorrections are applied to the next one or more lines. Multiple lines ofSOL to EOL time measurements can be averaged to reduce noise.

Based on the stripe divider and SOL/EOL peripheral reference marks, thepositioning of the servo beam 130 on the screen 101 can be measured.Because the servo beam 130 has a fixed relation with each excitationbeam 120, which can be measured at the SOL reference mark or EOLreference mark, any error in the positioning of the servo beam 130suggests a corresponding error in each excitation beam 120. Therefore,the positioning information of the servo beam 130 can be used in theservo control to control the servo beam 130 and each excitation beam 120to reduce an alignment error of the excitation beam.

The present servo control operates to place each optical pulse in theexcitation beam 120 near or at the center of a target light-emittingstripe to excite the light-emitting material in that stripe withoutspilling over to an adjacent light-emitting stripe. The servo controlcan be designed to achieve such alignment control by controlling thetiming of each optical pulse in order to place the pulse at a desiredposition on the screen 101 during a horizontal scan. Accordingly, theservo control, i.e., the processor and controller 640, needs to “know”horizontal positions of the light-emitting stripes in each horizontalline before each horizontal scan in order to control the timing ofoptical pulses during the scan. This information on horizontal positionsof the light-emitting stripes in each horizontal line constitutes atwo-dimensional position “map” of the active display area orlight-emitting area of the screen 101 of (x, y) coordinates where x isthe horizontal position of each stripe divider (or equivalently, thehorizontal position of the center of each stripe) and y is the verticalposition or ID number of a horizontal scan. This position map of thescreen 101 can be measured at the factory and may change in time due tochanges in the system components due to temperature, aging and otherfactors. For example, thermal expansion effects, and distortions in theoptical imaging system will need corresponding adjustments in theprecise timing to activate each color in a pixel. If the laser actuationdoes not properly correspond to the timing where the beam is directed atthe central portion of a sub-pixel or stripe for the intended phosphor,the beam 120 will either partially or completely activate the wrongcolor phosphor. In addition, this position map of the screen 101 canvary from one system to another due to the component and devicetolerances during the manufacturing.

Therefore, it is desirable to update the position map of the screen 101and to use the updated position map for controlling the timing of pulsesof the excitation beam 120 in each horizontal scan during the normaldisplay. The position map of the screen 101 can be obtained using thefeedback light 122 and 132 in a calibration scanning when the system isnot in the normal display mode, e.g., during the start-up phase of thesystem. In addition, the servo feedback light 132 can be used in realtime video display to monitor and measure changes in an existingposition map of the screen 101 when the system is operating in thenormal display mode to produce images on the screen 101. This mode ofthe servo control is referred to as dynamic servo. The dynamicmonitoring of the screen 101 can be useful when the system operates foran extended period time without a downtime because the screen 101 mayundergo changes that can lead to significant changes to the position mapof the screen 101 that is updated during the start-up phase of thesystem.

The position map of the screen 101 can be stored in the memory of thelaser module 110 and reused for an interval of time if the effects thatare being compensated for do not change significantly. In oneimplementation, when the display system is turned on, the display systemcan be configured to, as a default, set the timing of the laser pulsesof the scanning laser beam based on the data in the stored position map.The servo control can operate to provide the real-time monitoring usingthe servo feedback light 132 and to control the pulse timing during theoperation.

In another implementation, when the display system is turned on, thedisplay system can be configured to, as a default, to perform acalibration using the excitation beam 120 and the servo beam 130 to scanthrough the entire screen 101. The measured position data are used toupdate the position map of the screen 101. After this initialcalibration during the start-up phase, the system can be switched intothe normal display mode and, subsequently during the normal displayoperation, only the servo beam 130 is used to monitor the screen 101 andthe data on the screen 101 obtained from the servo beam 130 can be usedto dynamically update the position map and thus to control the timing ofpulses in the beam 120 in each horizontal scan.

The calibration of the position map of the screen 101 can be obtained byoperating each scanning beam 120 or 130 in a continuous wave (CW) modefor one frame during which the scanning laser beams 120 and 130simultaneously scan through the entire screen, one segment at a time asshown in FIG. 5, when multiple laser beams 120 are used. If a singlelaser is used to produce one excitation beam 120, the single scanningbeam 120 is set in the CW mode to scan the entire screen 101, one lineat a time, along with the servo beam 130. The feedback light 122 and 132from the servo reference marks on the stripe dividers is used to measurethe laser position on the screen 101 by using the servo detectors 620and 630.

The servo detector signals from the servo detectors 620 and 630 can besent through an electronic “peak” detector that creates an electronicpulse whenever a servo signal is at its highest relative amplitude. Thetime between these pulses can be measured by a sampling clock in adigital circuit or microcontroller that is used by the processor andcontroller 640 to process and generate an error signal for controllingtiming of optical pulses in each excitation beam 120 in a horizontalscan.

In one implementation, the time between two adjacent pulses from theelectronic peak detector can be used to determine the spacing of the twolocations that produce the two adjacent electronic pulses based on thescan speed of the scanning beam 120 or 130 on the screen 101. Thisspacing can be used to determine the subpixel width and subpixelposition.

In another implementation, servo measurements and corrections are basedon relative time measurements. Depending on the beam scan rate and thefrequency of the sampling clock, there are some nominal number of clocksfor each sub-pixel. Due to optical distortions, screen defects orcombination of the distortions and defects, the number of clock cyclesbetween two adjacent pulses for any given sub-pixel may vary from thenominal number of clock cycles. This variation in clock cycles can beencoded and stored in memory for each sub-pixel. Alternatively, acorrection value can be calculated and used for some number N ofadjacent sub-pixels because changes usually do not occur withsignificant changes between adjacent sub-pixels.

FIG. 15 shows one example of the detected reflected feedback light as afunction of the scan time for a portion of one horizontal scan, therespective output of the peak detector and the sampling clock signal. Anominal subpixel with a width corresponding to 9 clock cycles of thesampling clock and an adjacent short subpixel corresponding to 8 clockcycles are illustrated. In some implementations, the width of a subpixelmay correspond to 10-20 clock cycles. The clock cycle of the samplingclock signal of the digital circuit or microcontroller for the servocontrol dictates the spatial resolution of the error signal. As anexample for techniques to improve this spatial resolution, averagingover many frames can be utilized to effectively increase the spatialresolution of the error signal.

FIG. 16 shows one example of the detected reflected feedback light as afunction of the scan time for a portion of one horizontal scan, therespective output of the peak detector and the sampling clock signalwhere a nominal subpixel corresponding to a width of 9 clock cycles andan adjacent long subpixel a corresponding to a width of 10 clock cyclesre illustrated.

During calibration, contaminants such as dust on the screen, screendefects, or some other factors may cause missing of an optical pulse inthe reflected feedback light that would have been generated by a servoreference mark between two adjacent subpixels on the screen 101. FIG. 17illustrates an example where a pulse is missing. A missing pulse can bedetermined if a pulse is not sampled or detected within the nominalnumber of clock cycles for a subpixel within the maximum expecteddeviation from the nominal number of clocks for a subpixel. If a pulseis missed, the nominal value of clock cycles for a subpixel can beassumed for that missing sub-pixel and the next sub-pixel can containthe timing correction for both sub-pixels. The timing correction can beaveraged over both sub-pixels to improve the detection accuracy. Thismethod may be extended for any number of consecutive missed pulses.

The above use of the sampling clock signal to measure the position mapof the screen 101 can be used with detection with the excitation servofeedback light 122 or the servo feedback light 132 from the screen 101.Because the excitation beam or beams 120 scan all horizontal lines inthe screen 101 during a calibration scan in a CW mode, the position datafrom the excitation servo feedback light 122 can provide data for eachand every subpixel of the screen 101. The position data obtained fromthe servo beam 130 and its corresponding feedback light 132, however,only covers one horizontal scan line per screen segment as shown in FIG.5. The position data measured from the servo beam 130 for one screensegment can be used as a representative scan for all horizontal lines inthat screen segment is used to update position data for all lines inthat screen segment. Two or more servo beams 130 may be used to increasethe number of lines measured in each screen segment.

Vertical position of each laser can be monitored and adjusted by usingan actuator, a vertical scanner, an adjustable lens in the optical pathof each laser beam or a combination of these and other mechanisms.Vertical reference marks can be provided on the screen to allow for avertical servo feedback from the screen to the laser module. One or morereflective, fluorescent or transmissive vertical reference marks can beprovided adjacent to the image area of the screen 101 to measure thevertical position of each excitation beam 120. Referring to FIG. 11,such vertical reference marks can be placed in a peripheral referencemark region. One or more vertical mark optical detectors can be used tomeasure the reflected, fluorescent or transmitted light from a verticalreference mark when illuminated by the beam 120 or 130. The output ofeach vertical mark optical detector is processed and the information onthe beam vertical position is used to control an actuator to adjust thevertical beam position on the screen 101.

FIG. 18A shows an example of a vertical reference mark 2810. The mark2810 includes is a pair of identical triangle reference marks 2811 and2812 that are separated and spaced from each other in both vertical andhorizontal directions to maintain an overlap along the horizontaldirection. Each triangle reference mark 2811 or 2812 is oriented tocreate a variation in the area along the vertical direction so that thebeam 120 partially overlaps with each mark when scanning through themark along the horizontal direction. As the vertical position of thebeam 120 changes, the overlapping area on the mark with the beam 120changes in size. The relative positions of the two marks 2811 and 2812defines a predetermined vertical beam position and the scanning beamalong a horizontal line across this predetermined vertical positionscans through the equal areas as indicated by the shadowed areas in thetwo marks 2811 and 2812. When the beam position is above thispredetermined vertical beam position, the beam sees a bigger mark areain the first mark 2811 than the mark area in the second mark 2812 andthis difference in the mark areas seen by the beam increases as the beamposition moves further up along the vertical direction. Conversely, whenthe beam position is below this predetermined vertical beam position,the beam sees a bigger mark area in the second mark 2812 than the markarea in the first mark 2811 and this difference in the mark areas seenby the beam increases as the beam position moves further down along thevertical direction.

The feedback light from each triangle mark is integrated over the markand the integrated signals of the two marks are compared to produce adifferential signal. The sign of the differential signal indicated thedirection of the offset from the predetermined vertical beam positionand the magnitude of the differential signal indicates the amount of theoffset. The excitation beam is at the proper vertical position when theintegrated light from each triangle is equal, i.e., the differentialsignal is zero.

FIG. 18B shows a portion of the signal processing circuit as part of thevertical beam position servo feedback control in the laser module 110for the vertical reference mark in FIG. 18A. A PIN diode preamplifier2910 receives and amplifies the differential signal for the tworeflected signals from the two marks 2811 and 2812 and directs theamplified differential signal to an integrator 2920. Ananalog-to-digital converter 2930 is provided to convert the differentialsignal into a digital signal. A digital processor 2940 processes thedifferential signal to determine the amount and direction of theadjustment in the vertical beam position and accordingly produces avertical actuator control signal. This control signal is converted intoan analog control signal by a digital to analog converter 2950 and isapplied to a vertical actuator controller 2960 which adjusts theactuator. FIG. 18C further shows generation of the differential signalby using a single optical detector.

FIG. 19 shows an example of the screen in FIG. 11 having the start ofline (SOL) reference mark and the vertical beam position referencemarks. Multiple vertical beam position reference marks can be placed atdifferent vertical positions to provide vertical position sensing of theexcitation beams 120 in all screen segments. The example in FIG. 19shows the SOL reference mark is located between the vertical beamposition reference marks and the screen display area so that, in ahorizontal scan beginning from the left to the right, the excitationbeam 120 or the servo beam 130 hits the SOL reference mark after thevertical beam position reference marks. In another implementation for ahorizontal scan beginning from the left to the right, the SOL referencemark is located between the vertical beam position reference marks andthe screen display area to ensure that the excitation beam 120 or theservo beam 130 hits the SOL reference mark before the vertical beamposition reference marks. In addition, separate from the vertical beamposition reference marks for the excitation beams 120, multiple verticalbeam position reference marks can be placed at different verticalpositions, e.g., one vertical reference mark for the servo beam 130 toprovide vertical position sensing of the servo beam 130 in each screensegment. These vertical reference marks are presented by the numeral“1910” in FIG. 19. The combination of the SOL reference 1210, thevertical reference marks 1910 and the periodic pattern in the stripstructure of the light-emitting area 1110 provides positioninginformation of the invisible servo beam 130, positioning information ofthe excitation beams 120 and the horizontal parameters of the pixels onthe screen 101 for servo control in a scanning display system.

FIG. 20 shows an example of the operation of a servo control using theservo beam 130 during the normal display mode when each excitation beam120 is used for carrying optical pulses for producing images on thescreen 101 and is not used for servo control. The servo beam 130 is a CWbeam and is scanned over one horizontal line per screen segment with thescanning modulated excitation Laser beams 120. The servo feedback light132 is detected by the one or more servo detectors 620 to measure analignment error of the servo beam 130 on the screen 101 during thenormal display. The alignment of each excitation laser beam 120 isadjusted based on the measured alignment error of the servo beam 130 toreduce the alignment error of the excitation laser beam 120. In otherimplementations, the red, green and blue light emitted by the screen 101or a portion of back-reflected excitation light of the scanningexcitation beam 120 can be used to provide a calibration mechanism tocalibrate the measurements obtained via the servo beam 130.

In the above examples for using the invisible IR servo beam 130 toprovide the feedback light 132 to the laser module 110, the parallelphosphor stripes and the stripe dividers on the screen 101 are used toproduce back-reflected feedback light 132 by reflection of the servobeam 132 at the stripe dividers. Alternatively, the screen 101 can bedesigned to include IR feedback marks that are configured to producedesired feedback light 132. The IR feedback marks can be registered witha special spatial relationship with respect to the stripe dividers orthe phosphor stripes, e.g., a servo feedback mark is aligned in positionwith a light-emitting stripe or a division (a divider) between twoadjacent parallel light-emitting stripes in the screen. In the examplesdescribed below, such position registration is not required and it issufficient that the IR feedback marks have a fixed and known spatialrelationship with respect to the stripe dividers or the phosphor stripesso that there is a fixed and known mapping of the positions of the IRfeedback marks and the positions of the phosphor stripes and stripedividers.

FIG. 21 shows an example design for the light-emitting screen 101 thatincludes IR feedback marks on the excitation side of the phosphor layer.This screen 101 includes a phosphor stripe layer 2110 with parallelphosphor stripes emitting red, green and blue light under excitation ofthe excitation beam 120, a back panel 2112 on the excitation side of thephosphor layer 2110 facing the excitation beam 120 and the IR servo beam130, and a front panel 2111 on the viewer side of the phosphor layer2110. In this example, IR feedback marks 2120 are formed on the backsurface of the back panel to provide the IR feedback light 132 byreflecting or scattering the IR servo beam 130. In otherimplementations, the IR feedback marks 2120 may be placed at otherpositions and can be located on either the excitation side or the viewerside of the phosphor layer 2110.

The IR feedback marks 2120 are designed to provide position registrationof the servo beam 130 on the screen and can be implemented in variousconfigurations. For example, the IR feedback marks 2120 can be periodicparallel stripes that are parallel to the parallel phosphor stripes inthe phosphor layer 2110. An IR feedback mark 2120 can be placed at anyposition relative to a stripe divider or a phosphor stripe in thephosphor layer 2110 along the horizontal direction, including a positionhorizontally displaced from a stripe divider or the center of a phosphorstripe. The width of each of the IR feedback marks 2120 can be equal tothe width of the beam spot of the IR servo beam 130 on the screen 101when the detection for the IR servo feedback light 132 is based on apeak detector. IR feedback marks 2120 with a width wider than the widthof the beam spot of the IR servo beam 130 on the screen 101 can be usedif the detection for the IR servo feedback light 132 is based on theposition of each IR feedback mark 2120 with respect to a positionreference such as the SOL mark. The width of the IR feedback marks 2120may be less than the width of each phosphor stripe, e.g., one half ofthe width of a phosphor stripe. The spacing between two adjacent IRfeedback marks 2120 can be greater than the spacing between two adjacentphosphor stripes. For example, the IR mark spacing can be 25 mm and thephosphor stripe spacing can be 1.5 mm.

The IR feedback marks 2120 can be made to be optically different fromthe areas surrounding and between the IR feedback marks 2120 to allowfor optical detection of the IR feedback marks 2120 to register thepositions of the IR feedback marks 2120 on the screen while maintainingthe substantially the same optical transmission for the excitation beam120 as the areas surrounding and between the IR feedback marks 2120.Therefore, the presence of the IR feedback marks 2120 does not opticallyinterfere with the optical transmission of the excitation beam 120 byoptically imprinting the shapes of the marks 2120 on the excitation beam120 that reaches the phosphor layer of the screen 101. In this regard,the IR feedback marks 2120 can be implemented in various configurations.For example, each IR feedback mark 2120 can be made to have a smoothsurface facing the excitation side and optically specularly reflectiveto light and the areas surrounding and between the IR feedback marks2120 are configured to exhibit optically diffused reflection whichspreads in different directions. The specularly reflective IR feedbackmarks 2120 and the diffusively reflective areas surrounding and betweenthe marks 2120 have the same optical transmission characteristics.Different from the above design of having specularly reflective marks2120 in a diffusive background, the IR feedback marks 2120 can also bemade diffusively reflective to light and the areas surrounding andbetween the marks 2120 are made specularly reflective. As anotherexample, the IR feedback marks 2120 can have a transmissivity orreflectivity at the wavelength of the excitation beam 120 that issignificantly different from the wavelength of the servo beam and servowavelengths. For example, the IR feedback marks 2120 can be configuredto be optically transparent to light of the excitation beam 120 andoptically reflective to light of the servo beam 130 so that the IRfeedback marks 2120 are optically “invisible” to the excitation beam 120and reflect the servo beam 130 to produce the IR servo feedback light132.

FIGS. 22 and 23 show examples of screen layout configurations withvertical reference marks 1910 for measuring the vertical positions ofthe IR servo beam 130. In FIG. 22, the vertical reference marks 1910 arelocated on the edge of the screen, preferable outside the main displayarea of the screen. In FIG. 23, the vertical reference marks 1910 areplaced at the edges and in the middle of the screen and may be made tohave the same optical transmission characteristics for light of theexcitation beam 120.

FIG. 24 shows a specific example of a screen design with specularlyreflective IR feedback marks and optically diffusive areas surroundingand between the IR feedback marks. In this example, an IR feedback markis formed by a film stripe that has a smooth surface to produce aspecular reflection 2430 of the incident IR servo light 130. The screenarea between two IR feedback marks is formed by a film layer with aroughened surface that diffuses light in reflecting the incident IRservo light 130 to produce the diffused reflection 2440 that spreads indifferent directions forming a diffused reflection cone. The two regions2410 and 2420 have approximately the same optical transmission for lightof the excitation beam 120.

The above screen design for IR servo feedback can use the differentoptical behaviors of the specular reflection and the diffusivereflection of the IR servo beam 130 from the screen in the optical farfield from the screen to facilitate the servo detection as shown in theexample in FIG. 25.

FIG. 25 shows an exemplary scanning beam display system 2500 thatprovides an IR servo feedback based on the screen design in FIG. 24. Thelaser module 110 projects and scans both the IR servo beam 130 and theexcitation beam 120 onto the screen 101 with IR feedback marks. Thelaser module 110 has a symmetric optic axis 2501 around which the beamscanning is performed. The screen 101 has a construction as shown inFIG. 21 or 22 based on the design in FIG. 24. An optical telecentriclens 2510 such as a Fresnel lens layer is provided in to couple theincident scanning beams 120 and 130 from the laser module 110 onto thescreen 101 in a substantially normal incidence to the screen 101. Thetelecentric lens 2510 is configured to have its symmetric optic axis2502 to be parallel to the optic axis 2501 of the laser module 110 withan offset 2503. As illustrated, the Fresnel lens 2510 is placed in frontof the back surface of the screen 101 with an air gap 2520.

The IR servo detection is provided by using an IR servo detector 2530located along an optical path of the returned specular reflection 2430of the incident IR servo light 130 from the IR feedback marks on thescreen 101. The location of the IR servo detector 2530 is determined bythe offset 2503 for receiving the returned specular reflection 2430 ofthe incident IR servo light 130 from each IR feedback mark on the screen101. Returned IR light in a direction different from the specularreflection direction at each IR feedback mark is directed by the Fresnellens 2510 to miss the IR servo detector 2530 when the deviation from thespecular reflection exceeds a range beyond the aperture of the IR servodetector 2530. Under this design, only a very small fraction of thereturned IR servo light in the diffused reflection 2440 from an areabetween IR feedback marks is received by the IR servo detector 2530 andthe majority of the returned IR servo light in the diffused reflection2440 is not collected by the IR servo detector 2530. In contrast, thelight in the returned specular reflection 2430 of the incident IR servolight 130 from each IR feedback mark on the screen 101 is substantiallycollected by the IR servo detector 2530. Based on this difference, thedetector signals from the IR servo detector 2530 can be used todetermine a hit by the scanning IR servo beam 130 on an IR feedbackmark.

The light of the excitation beam 120 can also be reflected back by thespecular and diffusive regions on the screen 101. Hence, the specularlyreflected light at the excitation wavelength is directed back to thesame location at the IR servo detector 2530. A wavelength selectiveoptical beam splitter can be used to split the collected light at theservo wavelength and the collected light at the excitation wavelengthinto two separate signals for separate optical detectors, the IR servodetector 2530 to receive the IR servo light and another servo detectorto receive the feedback light at the excitation wavelength.

The scanning IR servo beam 130 can be a CW beam. As such, each hit at anIR feedback mark on the screen produces an optical pulse at the IR servodetector 2530. In each horizontal scan, the IR servo detector 2530detects a sequence of optical pulses that correspond to the different IRfeedback marks on the screen, respectively. The detector output of theIR servo detector 2530 is similar to the detector outputs shown in FIGS.13-17 obtained by using phosphor strip dividers as IR feedback marksexcept that the pulse separation in the detector output of the IR servodetector 2530 in time is greater and corresponds to the IR feedback markspacing. Similarly, SOL or EOL signals can be used to determine thehorizontal location of the scanning IR servo beam 130 and verticalreference marks can be used to determine the vertical position of thescanning IR servo beam 130.

In the system examples in FIGS. 1, 6 and 7, the excitation servofeedback light 122 can be used in combination with the servo feedbackbased on invisible servo beam 130. In such systems with combinationservo controls, the positioning measurements from both the IR servolight feedback and the excitation light servo feedback can be used tocalibrate with respect to each other. For example, such a display systemcan be operated to perform a calibration using the excitation beam 120and the IR servo beam 130 to scan through the entire screen 101 tomeasure the position maps of the screen 101 and to use the position mapobtained from the excitation beam 120 to calibrate the position mapobtained from the IR servo beam 130. Based on this calibration, duringthe normal operation of the system, the feedback from the IR servo beam130 can be used, without the feedback based on the excitation lightservo feedback, to monitor the screen 101 and to control the timing ofpulses in the beam 120 in each horizontal scan.

In some implementations, the screen 101 can be designed to utilize asmuch the excitation light for producing the visible light by reducingany optical loss of the excitation light from the excitation beam 120.For example, the screen can be designed to eliminate any opticalreflection back to the laser module 110 by using, e.g., an optical layeron the excitation side of the phosphor layer to transmit light of theexcitation beam into the phosphor layer and recycle any excitation lightfrom the phosphor layer back into the phosphor layer. Under such adesign, it can be difficult to use light from the excitation beam 120 toproduce the servo beam 122. The following sections describe systemdesigns that use visible light emitted by the phosphor layer in thescreen 101 to produce a visible servo beam and to provide a secondfeedback mechanism in addition to the invisible IR servo feedback.

FIG. 26 shows an example of a scanning beam display system 2600 thatprovides the servo feedback based on the IR servo beam 130 and a secondservo feedback based on detection of emitted visible light from thephosphor layer in the screen. In this system, an off-screen opticalservo sensing unit 2610 is used to detect the red, green and blue lightemitted from the screen 101. The servo sensing unit 2610 can be locatedat a location where the emitted visible light from the screen 101 can bedetected, e.g., at the viewer side of the screen 101 or at theexcitation side of the screen 101 as shown, and the location of theservo sending unit 2610 can be selected based on the screen design andthe system layout. Three optical detectors PD1, PD2 and PD3 are providedin the sensing unit 2610 to detect the red, green and blue fluorescentlight, respectively. Each optical detector is designed to receive lightfrom a part of or the entire screen 101. A bandpass optical filter canbe placed in front of each optical detector to select a designated colorwhile rejecting light of other colors. This sensing unit 2610 generatesa servo feedback signal 2612 to the laser module 110 for controlling thesystem operation.

One way to correct the horizontal misalignment in the display systems inFIG. 26 is to program the display processor in the laser module 110 tocontrol the timing of the optical pulses based on the position errordetected in the feedback signal 2612. For example, the laser module 110can delay the modulated image signal carried by the modulated laser beam120 by one sub color pixel time slot if the green detector has an outputand red and blue detectors have no output or by two sub color pixel timeslots if the blue detector has an output and red and green detectorshave no output. This correction of a spatial alignment error by a timedelay may be achieved digitally within the display processor. Nophysical adjustment in the optical scanning and imaging units in thelaser module 110 is needed. Alternatively, you mean the controller unitin the laser module 110 may be adjusted to physically shift the positionof the excitation beam 120 on the screen 101 so that the laser positionon the screen 101 is adjusted horizontally to the left or right by onesub pixel in response to the error detected by the servo sensing unit2610. The optical alignment by physically adjusting the scanning laserbeam 120 and the electronic or digital alignment by controlling thetiming of optical pulses can be combined to control the properhorizontal alignment.

A test pattern can be used to check the horizontal alignment in thedisplay system 2600 in FIG. 26. For example, a frame of one of the red,green and blue colors may be used as a test pattern to test thealignment. FIG. 27A shows a test pattern for the color pixel embeddedwith the detectors in the servo sensing unit 2610 and the correspondingoutputs of the three detectors PD1, PD2 and PD3 when the horizontalalignment is proper without an error. FIGS. 27B, 27C and 27D show threedifferent responses generated by the three detectors PD1, PD2 and PD3when there is a misalignment in the horizontal direction. The detectorresponses are fed to the laser module 110 and are used to either use thetime-delay technique or the adjustment of the beam imaging optics tocorrect the horizontal misalignment.

Hence, the servo feedback control based on sensing the screen-emittedvisible light in FIG. 26 is operated in during a designated calibrationoperation of the system 2600 when the system 2600 is not displayingimages for the viewer. This type of feedback control is “static” becausethe system is operated out of its normal display mode and is operatedwith test patterns for measuring the alignment conditions of the screen101. For example, such a static servo feedback algorithm can beperformed once at the power-on of the display system or at the factoryinitial map generation before the system begins the normal display ofthe images on the screen 101 and the display system can be controlled toperform the initial clock calibration to align the laser pulses to thesub-pixel center positions. Different from the static servo control, adynamic servo control can also be implemented during the normal displayoperation mode of the system. For example, the dynamic servo feedbackalgorithm is performed continuously during the normal operation of thedisplay system. This dynamic servo feedback keeps the pulses timed tothe subpixel center position against variations in temperature, screenmotion, screen warping, system aging and other factors that can changethe alignment between the laser and the screen. The dynamic servocontrol is performed when the video data is displayed on the screen andis designed in a way that it is not apparent to the viewer. This dynamiccontrol is provided by the invisible servo control in the system 2600 inFIG. 26.

FIG. 28 illustrates an example of an optical servo design using avisible light servo optical sensor 4501 placed away from a fluorescentscreen 101 on the viewer side of the screen 101 in the scanning beamdisplay system 2600. The optical sensor 4501 may be configured andpositioned to have a field of view of the entire screen 101. Acollection lens may be used between the screen 101 and the sensor 4501to facilitate collection of the fluorescent light from the screen 101.The optical sensor 4501 can include at least one optical detector todetect fluorescent light at a selected color, e.g., green from differentcolors (e.g., red, green and blue) emitted by the screen 101. Dependingon the specific techniques used in the servo control, a single detectorfor a single color may be sufficient for the servo control in someimplementations and, in other implementations, two or more opticaldetectors for detecting two or more colors of the fluorescent light fromthe screen 101 may be needed. Additional detectors may be used toprovide detection redundancy for the servo control. Referring to thereference marks for generating reference signals, detection of suchreference signals and control functions based on the reference signalsfrom reference marks, the servo control can be combined with the controlfunctions of the reference marks for the system. In an example describedbelow, the start of line reference mark outside the screen area havingthe fluorescent stripes can be used as a timing reference for staticservo control of the timing of optical pulses of the scanning beam.

In the example in FIG. 28, the optical sensor 4501 includes three servooptical detectors 4510, 4520 and 4530 (e.g., photodiodes) that detect,respectively, three different colors emitted by the screen 101. Thephotodiodes 4510, 4520 and 4530 are arranged in three groupings and eachgroup is filtered by a red filter 4511, a green filter 4521 or a bluefilter 4531 so that three photodiodes 4510, 4520 and 4530 receive,respectively, three different colors. Each filter may be implemented invarious configurations, such as a film which makes a photodiodesensitive only to one of the red, green and blue colors from the viewingscreen.

The detector circuit for each color group can include a preamplifier(preamp) 4540, a signal integrator (e.g., a charge integrator) 4541, andan A/D converter 4540 to digitize the red, green or blue detector signalfor processing in a digital servo circuit 4550 which may be amicrocomputer or microprocessor. The red, green and blue lightintensities of the fluorescent light emitted from the screen 101 can bemeasured and the measured results are sent to the digital servo circuit4550. The digital servo circuit 4550 can generate and use a reset signal4552 to reset the integrators 4541 to control the integration operationof the detectors. Using these signals, the digital servo circuit 4550can determine whether there is an error in the alignment of a scanninglaser beam on the screen 101 and, based on the detected error,determines whether the laser clock is to be advanced or delayed in timein order to center the laser pulses on the subpixels on the screen 101.

The static servo control operations described here are performed whenthe display system is not in the normal operation for displaying imageson the screen. Hence, the regular frame scanning in both directionsusing the galvo vertical scanner and the polygon horizontal scannerduring the normal operation can be avoided. The vertical scanning by thegalvo scanner can be used to direct a scanning laser beam at a desiredvertical position and fixed at that position to perform repetitivehorizontal scans with different time delays in the laser pulse timing toobtain the desired error signal indicating the laser timing error in thehorizontal scan. In addition, a special laser pulse pattern (e.g., FIGS.27A-D and 29) that does not carry image signals can be used during thestatic servo operation to generate the error signal.

In the static servo control, the laser pulse pattern for a laser can bechosen to generate a signal that is proportional to the position errorof the laser pulses on the screen 101. In one implementation wheremultiple lasers are used, each laser is pulsed one at a time across thescreen 101 and the remaining lasers are turned off. This mode ofoperation allows the timing for each laser to be measured and correctedindependently during a static servo control process.

FIGS. 29 and 30 illustrate one example technique for generating theerror signal for implementing the static servo control. FIG. 29 shows anexample of a test optical pulse pattern modulated onto a scanning laserbeam that has a periodic pulse pattern of laser pulses. The pulse widthin time of this test pulse pattern corresponds to a spatial width on thescreen that is greater than the width (d) of the border between twoadjacent subpixels and less than twice of the width (D) of a subpixel(one fluorescent stripe). For example, the pulse width in time of thispulse pattern corresponds to a spatial width equal to the width (D) of asubpixel. The repetition time of the pulse pattern corresponds to aspatial separation of two adjacent laser pulses on the screen that isequal to the width (3D) of one color pixel (three successive fluorescentstripes).

In operation, the timing of the laser pulse pattern in FIG. 29 isadjusted so that each laser pulse partially overlaps with one subpixeland an adjacent subpixel to excite light of different colors in the twoadjacent subpixels. Hence, a laser pulse overlapping with two adjacentsubpixels (e.g., a red subpixel and a green subpixel) has a redexcitation portion that overlaps with the red subpixel to produce redlight and a green excitation portion that overlaps with the adjacentgreen subpixel to produce green light. The relative power levels of theemitted red light and the emitted green light are used to determinewhether the center of the laser pulse is at the center of the borderbetween two adjacent subpixels and the position offset between thecenter of the laser pulse and the center of the border. Based on theposition offset, the servo control adjusts the timing of the laser pulsepattern to reduce the offset and to align the center of the laser pulseat the center of the border. Upon completion of this alignment, theservo control advances or delays the timing of the laser pulse patternto shift each laser pulse by one half of the subpixel width to place thecenter of the laser pulse to the center of either of the two adjacentsubpixels. This completes the alignment between a laser and a colorpixel. During the above process, the vertical scanner is fixed to directthe laser under alignment to a fixed vertical position and thehorizontal polygon scanner scans the laser beam repetitively along thesame horizontal line to generate the error signal.

The above process uses the relative power levels of the emitted redlight and the emitted green light to determine position offset betweenthe center of the laser pulse and the center of the border between twoadjacent subpixels. One way to implement this technique is to use adifferential signal based on the difference in the amounts of lightemitted by the two different phosphor materials. A number of factors inthe servo detection in FIG. 28 can affect the implementation. Forexample, different fluorescent materials for emitting different colorsmay have different emission efficiencies at a given excitationwavelength so that, under the same scanning excitation beam, twoadjacent subpixels can emit light in two different colors (e.g., greenand red) with different power levels. As another example, the colorfilters 4511, 4521 and 4531 for transmitting red, green and blue colorsmay have different transmission values. As yet another example, theoptical detectors 4510, 4520, and 4530 may have different detectorefficiencies at the three different colors and thus for the same amountof light entered into the detectors at different colors, the detectoroutputs may be different. Now consider the condition where the center ofa laser pulse is aligned to the center of the border between twoadjacent subpixels and thus the laser pulse is equally spit between thetwo adjacent subpixels. Due to the above and other factors, the servooptical detectors corresponding to the emission colors of the twoadjacent subpixels may produce two detector outputs of two differentsignal levels when the laser pulse is equally spit between the twoadjacent subpixels. Hence, for a given display system, the servodetector signals can be calibrated to account for the above and otherfactors to accurately represent the position offset of the laser pulse.The calibration can be achieved via the hardware design, software in thedigital signal processing in the servo digital circuit 4550 in FIG. 28,or a combination of both the hardware design and signal processingsoftware. In the following sections, it is assumed that the propercalibration is implemented so that the calibrated detector outputs fromtwo different servo optical detectors are equal when the laser pulse isequally spit between the two adjacent subpixels.

Therefore, under a proper alignment condition, each of the laser pulseshas one half of the pulse over a green subpixel, and the remaining onehalf of the same pulse over an adjacent red subpixel. This pulse patterngenerates equal amounts of red and green light on the servo detectorswhen the alignment is proper. Therefore, the difference in the detectoroutput voltage between the red detector and the green detector is anerror signal that indicates whether the alignment is proper. When thealignment is proper, the differential signal between the red and greendetectors is zero; and, when the alignment is off from the properalignment, the difference is either a positive value or a negative valueindicating the direction of the offset in alignment. This use of adifferential signal between two color channels can be used to negate theimportance of measuring the absolute amplitude of the light emanatedfrom the viewing screen phosphor. Alternatively, the difference betweentwo different color channels, the blue and red detectors or the greenand blue detectors, may also be used to indicate the alignment error. Insome implementations, because the blue light is closest to the incidentexcitation laser light wavelength, it can be more practical to use thedifference between the green and red detectors for the servo control. Anoptical sensor for detecting light from the reference mark, which isseparate from the optical sensor 4501 for detecting the fluorescentfeedback light from the screen in FIG. 28, is used to generate thedetection signal and is connected to the digital servo circuit 4550.

In the static servo control, the start of the timing scan can becorrected first using the test pulse pattern in the scanning laser beam.The timing is corrected for the first group of adjacent pixels along thehorizontal scan (e.g., 5 pixels), then the next group of adjacent pixelsof the same size, e.g., the next 5 group, then the next 5 group, untilthe entire scan has been corrected for a given laser. Here, the numberof 5 pixels is chosen as an example for illustration. Such grouping canbe used to reduce the amount of time needed for the servo control and toincrease the signal-to-noise ratio of the error signal when the signalsgenerated from different pixels in one group are integrated. Inpractice, the number of pixels for each of the groups can be selectedbased on specific requirements of the display system. For example, theseverity of the initial timing error may be considered where a smalltiming error may permit a large number of successive pixels to be in agroup for the servo control and a large timing error may require asmaller number of successive pixels to be grouped together for the servocontrol. In each measurement, the timing error of the scanning beam canbe corrected to one clock cycle of the digital clock of the digitalservo circuit 4550. In FIG. 45, digital servo circuit 4550 is amicro-controller which is designed to have timing control for eachindividual laser and is used to correct the timing of the laser pulsefor each pixel.

Notably, various phosphors can exhibit persistence in fluorescentemission. This property of phosphors can cause the phosphor to producelight after the laser pulse has moved to the next pixel. Referring toFIG. 28, the signal integrator 4541 can be connected at the output ofthe preamp 4540 for each servo detector to offset this effect of thephosphor. The integrator 4541 can be used to effectively “sum” all thelight for a given preamp 4540 over multiple pixels while the reset linefor the integrator is low to set the integrator in the integration mode.When the micro-controller initiates an A/D sample, the summed light fora given color is sampled. The reset line 4552 for each integrator 4541then goes high until the integrator voltage is set back to zero to resetthe integrator 4541 and is subsequently released back to low to restarta new integration period during which the integrator 4541 starts summingthe light again.

FIG. 30 illustrates how the error signal varies as the laser timing isvaried from its nominal position directly centered between the red andgreen subpixels using the laser pulse pattern in FIG. 29. When the errorvoltage of a differential signal based on the laser pulse pattern inFIG. 29 is equal to zero as shown in FIG. 30, there are equal amounts ofRed and Green light on the red and green servo detectors, and the timingof the laser pulses is directly over the borders between two adjacentsub-pixels. In this manner, the error signal at each sample representsthe laser timing error only for the period after the previous resetpulse. Using this scheme, a corrected laser timing map can be generatedfor each laser on every horizontal sweep until the entire screen timingis corrected for each laser. The vertical scanner is used to change thevertical position of the horizontal scanning beam from each laser.

The above technique for generating the static servo error signal uses aborder between the two adjacent subpixels as an alignment reference toalign the laser pulse in a laser pulse pattern. Alternatively, thecenter of each subpixel may be directly used as an alignment referenceto center the laser pulses directly over the subpixels without using theborders between two adjacent subpixels. Under this alternative method,the output from a single color servo optical detector is sufficient togenerate the error signal for the servo control. An alignment referencemark, such as the start of line (SOL) peripheral alignment referencemark in FIG. 12 and a separate SOL optical detector that detects thefeedback light from the SOL mark, can be used to provide a timingreference and assist the alignment. Referring to FIG. 45, the SOLoptical detector is connected to direct its output to the digital servocircuit 4550.

This alternative static servo technique can be implemented as thefollows. A test pulse pattern that has at least one pulse correspondingto one subpixel within a pixel used to modulate the scanning laser beamwhere the pulse width corresponds to one subpixel width (D) or less. Ina horizontal scan, the laser timing is adjusted on the first group ofsubpixels of the scan after the SOL signal is detected by the SOLoptical detector. Based on the timing reference from the SOL signal, thelaser timing of the laser pulse pattern is adjusted to maximize thedetected optical power of one of the three colors emitted by thefluorescent screen, e.g., the Green light (or Red, or Blue). Theadjustment can be achieved by pulsing the laser once per pixel andadjusting the laser timing. When the Green light is maximized on thefirst 5 pixels, the next five green subpixels are pulsed. The timing isadvanced by one clock cycle during one horizontal scan, then delayed byone clock cycle on subsequent laser horizontal scans at the samevertical position on the screen. The timing that produces the maximumGreen light is chosen as the correct laser timing. If the output signalfrom advancing the clock cycle is equal to the output signal formdelaying the clock cycle, then the laser timing is proper and is leftunchanged. The next 5 pixels are then illuminated with the advanced anddelayed laser clock cycles, and the timing that produces the maximumGreen light is chosen for this group of 5 pixels. This operation isrepeated across the horizontal length of the screen until the end of thescreen is reached. This method can also produce a laser clock that iscorrected for each laser as the beam from the laser sweeps horizontallyacross the screen.

The above static servo control operations are performed when the displaysystem is not in the normal operation and thus a test pulse pattern(e.g., FIG. 29) that does not carry image signals can be used. Thedynamic servo correction is performed by using the invisible IR servofeedback during normal operation and viewing of images on the screen.

On a given horizontal scan, all the lasers can be advanced in phase byone clock cycle of the digital circuit 4550. This operation causes allthe laser beams to shift in their positions on the screen by a scanningdistance over the one clock cycle and this shift is small when thescanning distance is small (e.g., less than one tenth of the subpixelwidth). Accordingly, the amplitude of the emitted color light from asubpixel (e.g., the green detector) is slightly changed. On the nextframe, all the lasers are delayed in phase by one clock cycle. If thenominal laser pulse position is initially correct, the amplitudes of thedelayed and advanced scans of the two different and successive imageframes should be equal for any color chosen to be measured and observed.When the amplitudes of the delayed and advanced scans of two differentframes are different, there is a laser timing error and a correction canbe applied to the laser timing to reduce the difference in subsequentimage frames while the error signal is being monitored and thecorrection is updated based on the newly generated error signal. Thesign of the difference indicates the direction of the offset in thelaser timing error so that the servo control can apply the correction tonegate the offset. Similar to the second static servo control methoddescribed above, the output from a single color servo optical detectoris sufficient to generate the error signal for the dynamic servocontrol.

FIG. 31 shows a more detailed example of a scanning beam system based onboth the dynamic invisible servo feedback and the visible light staticservo feedback. An IR servo detector 620 is provided on the excitationside of the screen 101 to detect the IR servo light 132 reflected fromthe screen 101 while visible light servo detectors 3110 are placed onthe viewer side of the screen 101 to detect screen-emitted visible light3120 to provide visible light servo detector signals that are fed intothe display processor and controller 640. The visible light static servofeedback is used to calibrate the position map of the dynamic IR servofeedback during a calibration run of the system and the calibrateddynamic IR servo feedback is used during normal operation of the systemto correct beam alignment errors.

While this patent application contains many specifics, these should notbe construed as limitations on the scope of an invention or of what maybe claimed, but rather as descriptions of features specific toparticular embodiments of the invention. Certain features that aredescribed in this patent application in the context of separateembodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or a variation of a subcombination.

Only a few implementations are disclosed. However, variations andenhancements of the described implementations and other implementationscan be made based on what is described and illustrated in this patentapplication.

For example, multiple sheets of films with different refractive indicesmay be laminated or fused together to construct a composite sheet as theD1 or D2 dichroic layer. In some implementations, multiple layers of twodifferent materials with different indices may be used to form acomposite film stack as D1 or D2 by placing the two materials in analternating manner. In other implementations, three or more differentmaterials with different indices may be stacked together to form thecomposite film stack as D1 or D2. Such a composite sheet for the D1layer is essentially, an optical n interference reflector that transmitsthe excitation light (e.g., UV light) that excites the phosphormaterials which emit colored visible light and reflects the coloredvisible light. A composite sheet for the D2 layer may be complementaryto the D1 layer transmitting the colored visible light emitted by thephosphors and reflecting the excitation light (e.g., UV light). Suchcomposite sheets may be formed of organic, inorganic or a combination oforganic and inorganic materials. The multiple-layer composite sheet maybe rigid or flexible. A flexible multi-layer composite sheet may beformed from polymeric, non-polymeric materials, or polymeric andnon-polymeric materials. Exemplary films including a polymeric andnon-polymeric material are disclosed in U.S. Pat. No. 6,010,751 entitled“Method for forming a multicolor interference coating” and U.S. Pat. No.6,172,810 entitled “Retroreflective articles having polymer multilayerreflective coatings” which are incorporated by reference in theirentirety as part of the specification of this application. Anall-polymer construction for such composite sheets may offermanufacturing and cost benefits. If high temperature polymers with highoptical transmission and large index differentials are utilized in theinterference filter, then an environmentally stable filter that is boththin and very flexible can be manufactured to meet the optical needs, ofshort-pass (SP) and (LP) filters. In particular, coextruded multilayerinterference filters as taught in U.S. Pat. No. 6,531,230 entitled“Color shifting film” can provide the precise wavelength selection aswell as a filter film in a large area based on cost effectivemanufacturing. The entire disclosure of U.S. Pat. No. 6,531,230 isincorporated by reference as part of the specification of thisapplication. The use of polymer pairs having high index differentialsallows the construction of very thin, highly reflective mirrors that arefreestanding, i.e. have no substrate but are still easily processed forconstructing; large screens. Such a composite sheet is functionally apiece of multi-layer optical film (MOF) and includes, e.g., alternatinglayers of PET and co-PMMA to exhibit a normal-incidence reflection bandsuitable for the screen applications of this application. As an example,an enhanced specular reflector (ESR) made out of a multilayerpolyester-based film from 3M Corporation may be configured to producethe desired dichroic reflection and transmission bands for the presentapplication. Examples for various features of multi-layer films aredescribed in U.S. Pat. No. 5,976,424 entitled “Method for makingmultilayer optical films having thin optical layers,” U.S. Pat. No.5,080,467 entitled “Biphenyl derivatives for photostabilization inpulsed optical darkening apparatus and method” and U.S. Pat. No.6,905,220 entitled “Backlight system with multilayer optical filmreflector,” all of which are incorporated by reference as part of thespecification of this application.

1-10. (canceled)
 11. A scanning beam display system, comprising: a lightmodule to direct and scan at least one excitation beam having opticalpulses that carry image information and at least one servo beam at aservo beam wavelength different from a wavelength of the excitationbeam; a screen positioned to receive the scanning excitation beam andthe servo beam, the screen comprising a light-emitting layer of parallellight-emitting stripes that absorb light of the excitation beam to emitvisible light to produce images carried by the scanning excitation beam,wherein an excitation side of the parallel light-emitting stripesincludes a plurality of diffusively reflective servo marks that arespaced apart from each other to diffusively reflect servo beam light toproduce servo feedback light, areas between the diffusively reflectiveservo marks including a specularly reflective region to specularlyreflect servo beam light; and an optical servo sensor module positionedon an excitation side of the screen to receive diffusively reflectedservo feedback light and to produce a servo feedback signal indicativeof positioning of the servo beam on the screen, wherein the light moduleis responsive to the servo feedback signal to adjust timing of theoptical pulses carried by the scanning excitation beam while beingscanned across the screen to control spatial positions of opticalexcitation beam pulses on the screen.
 12. The system as in claim 11,wherein the specularly reflective region is supported by a coextrudedfilm.
 13. The system as in claim 12, wherein the specularly reflectiveregion is part of the coextruded film.
 14. The system as in claim 11,wherein the diffusively reflective servo marks are surrounded by thespecularly reflective region.
 15. The system as in claim 11, wherein theplurality of diffusively reflective servo marks are positioned betweenthe parallel light-emitting stripes.
 16. The system as in claim 15,wherein the parallel light-emitting stripes are positioned on a viewerside of the specularly reflective region, and wherein the diffusivelyreflective servo marks are disposed on an excitation side surface of thespecularly reflective region.
 17. The system as in claim 16, wherein thespecularly reflective region is supported by a coextruded film.
 18. Thesystem as in claim 17, wherein the specularly reflective region is partof the coextruded film.
 19. The system as in claim 11, furthercomprising one or more additional optical servo sensor modules.
 20. Thesystem as in claim 11, wherein the servo beam is an IR beam.
 21. Thesystem as in claim 11, wherein the parallel light-emitting stripes aremade of phosphor materials.
 22. A method for controlling a scanning beamdisplay system, comprising: scanning one or more excitation beamsmodulated with optical pulses to carry image information across a screento excite parallel light-emitting strips to emit visible light whichforms an image; scanning a servo beam at an optical wavelength differentfrom an optical wavelength of the one or more excitation beams, acrossthe screen; detecting light of the servo beam that is diffusivelyreflected from a diffusively reflective servo mark on the screen toobtain a servo signal indicative of positioning of the servo beam on thescreen; and in response to the servo signal, controlling the one or morescanning excitation beams to control spatial positions of each opticalexcitation beam pulses on the screen.